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PubMed1975

Temporary expression of flagellar phase-1 in phase-2 clones of diphasic Salmonella.

Diphasic Salmonella strains, Salmonella typhimurium TM2, S. abony SW803 and their derivatives differing in flagellar shape and antigen type, were found to produce copolymer segments of phase-1 and phase-2 flagellins among flagella in phase 2, except for a strain which is non-flagellate in phase 1. The copolymer segments were not detected in phase-1 clones of any of the strains. The wave-forms of the copolymers are homologous with those of the copolymer filaments obtained by in vitro reconstitution of the corresponding phase-1 and phase-2 flagellins. Thus, in the mutant producing normal flagella in phase 1 and straight ones in phase 2, copolymer segments with curly or small waves appear among the straight filaments. Formation of the copolymers was attributed to temporary derepression of the structural gene for phase-1, flagellin, HI, in phase 2. Copolymerization occurred in a fraction of the phase-2 cell population at late exponential and early stationary phase in nutrient broth cultures. When a phase-2 cell was temporarily derepressed, the copolymers formed almost simultaneously in every growing flagellar filament of the cell. Their formation continued for a short period until the supply of phase-1 flagellin was exhausted after re-establishment of repression. This period was estimated to be 7-7 min on average, fluctuating between 4 and 13 min in a cell population of a straight flagellar mutant whose generation time was 55 min in late exponential phase.

Bacterial Proteins↗

PubMed1999

Misexpression of the opaque-phase-specific gene PEP1 (SAP1) in the white phase of Candida albicans confers increased virulence in a mouse model of cutaneous infection.

Candida albicans WO-1 switches reversibly and at high frequency between a white and an opaque colony-forming phenotype that includes dramatic changes in cell morphology and physiology. A misexpression strategy has been used to investigate the role of the opaque-phase-specific gene PEP1 (SAP1), which encodes a secreted aspartyl proteinase, in the expression of the unique opaque-phase phenotype and phase-specific virulence in two animal models. The PEP1 (SAP1) open reading frame was inserted downstream of the promoter of the white-phase-specific gene WH11 in the transforming vector pCPW7, and the resulting transformants were demonstrated to misexpress PEP1 (SAP1) in the white phase. Misexpression did not confer any of the unique morphological characteristics of the opaque phase to cells in the white phase and had no effect on the switching process. However, misexpression conferred upon white-phase cells the increased capacity of opaque-phase cells to grow in medium in which protein was the sole nitrogen source. Misexpression of PEP1 (SAP1) had no effect on the virulence of white-phase cells in a systemic mouse model, in which white-phase cells were already more virulent than opaque-phase cells. Misexpression did, however, confer upon white-phase cells the dramatic increase in colonization of skin in a cutaneous mouse model that was exhibited by opaque-phase cells. Misexpression of PEP1 (SAP1) conferred upon white-phase cells two dissociable opaque-phase characteristics: increased adhesion and the capacity to cavitate skin. The addition of pepstatin A to the cutaneous model inhibited the latter, but not the former, suggesting that the latter is effected by released enzyme, while the former is effected by cell-associated enzyme.

Animals↗

PubMed1994

Enigmatic thermotropic phase behavior of highly asymmetric mixed-chain phosphatidylcholines that form mixed-interdigitated gel phases.

Twelve saturated mixed-chain phosphatidylcholines have been identified for which the thermotropic phase behavior observed upon cooling from the L alpha phase is dependent upon the thermal history of the sample in the gel phase. If fully hydrated samples of these lipids are cooled and soon thereafter examined by differential scanning calorimetry, one observes a single highly cooperative endotherm (the chain-melting phase transition) upon heating, and on subsequent cooling, a single exotherm that may occur at temperatures as much as 4-6 degrees C below that of the single endotherm observed upon heating. In contrast, if the samples are incubated in the gel state at low temperatures for prolonged periods of time, one observes a single heating endotherm as before, but two sharp exotherms upon cooling. The latter transitions occur at temperatures close to that of the single endotherm observed upon heating and the single cooling exotherm observed prior to incubation in the gel state. The combined enthalpy of the two cooling exotherms is the same as that of the single heating endotherm or the single cooling exotherm initially observed. Infrared spectroscopic and X-ray diffraction studies indicate that the structural conversions characteristic of liquid-crystalline/gel phase transitions occur at both of those cooling exotherms. Of the 12 lipids that exhibit this unusual behavior, nine fulfill the previously defined structural requirements for the formation of the so-called mixed-interdigitated gel phase, and there is evidence in the literature that one of the three remaining lipids also forms such a structure. Infrared spectroscopic studies of the other two lipids indicate that their gel phases exhibit spectroscopic features that closely resemble those of lipids that meet the previously defined structural criteria for the formation of mixed-interdigitated gel phases and that differ markedly from those of both saturated symmetric-chain and saturated mixed-chain phosphatidylcholines that do not normally form mixed-interdigitated gel phases. Also, electron density reconstructions based on small-angle X-ray diffraction studies of the gel phases of those two lipids indicate that the thickness of their gel phase bilayers is consistent with their forming mixed-interdigitated gel phases. Thus the unusual thermotropic phase behavior described here may be a general characteristic of phosphatidylcholines that form mixed-interdigitated gel phases. This unusual behavior is not associated with any major change in any of several physical properties of these lipid bilayers but may arise from an alteration of the size and/or structure of microdomains present in the liquid-crystalline phase.

Gels↗

PubMed1992

Lateral diffusion and percolation in two-phase, two-component lipid bilayers. Topology of the solid-phase domains in-plane and across the lipid bilayer.

Fluorescence recovery after photobleaching (FRAP) has recently been used to examine the percolation properties of coexisting phases in two-component, two-phase phosphatidylcholine bilayers [Vaz, W. L. C., Melo, E. C. C., & Thompson, T. E. (1989) Biophys. J. 56, 869-876]. We now report the use of FRAP to study two additional problems in similar systems. The first is the effect of solid-phase obstacles on the lateral diffusion in the fluid phase. The second is the question of whether or not, in a single bilayer, solid-phase domains in one monolayer are exactly superimposed on solid domains in the apposing monolayer. To address the first problem, the lateral diffusion of N-(7-nitrobenzoxa-2,3-diazol-4-yl)-1-palmitoyl-2-oleoylphosp hatidylethanolamine (NBD-POPE), a probe soluble only in the fluid phase when solid and fluid phases coexist, has been studied in the mixture N-lignoceroyldihydrogalactosylceramide (LigGalCer)/dipalmitoylphosphatidylcholine (DPPC). Percolation of the fluid phase occurs at a high mass fraction of solid phase. This indicates that the solid domains have a centrosymmetric shape, a characteristic which makes this a good experimental system to test theoretical simulations of diffusion in an archipelago. It is shown that agreement between theory and experiment is poor, a result that had already been observed when the obstacles were integral membrane proteins. We develop an effective-medium model for diffusion in two-phase systems which explains both our results and those obtained with integral proteins. The distinctive feature of the model is the consideration of an annular region around the obstacles where the lipids are more ordered than in the bulk fluid phase. The diffusion coefficient is then calculated by extending the free area model to two-phase systems, taking these annuli into account. The second question, the organization of the solid-phase domains across the lipid bilayer, is examined in the systems LigGalCer/DPPC and dimyristoylphosphatidylcholine (DMPC)/distearoylphosphatidylcholine (DSPC) by comparing the diffusion of a fluid-phase-soluble, gel-phase-insoluble lipid derivative which spans the two monolayers of a bilayer (NBD-membrane-spanning-phosphatidylethanolamine, NBD-msPE) with that of a probe which is restricted to a single monolayer. In LigGalCer/DPPC, 20:80, the distribution of solid domains in one of the monolayers is independent of the distribution in the apposing monolayer. In contrast, in DMPC/DSPC, 50:50, the solid domains in one monolayer are exactly superimposed upon the solid domains existing in the apposing monolayer.

Diffusion↗

PubMed1991

Fluid-phase connectivity and translational diffusion in a eutectic, two-component, two-phase phosphatidylcholine bilayer.

In recent work [Vaz, W.L.C., Melo, E.C.C., & Thompson, T.E. (1989) Biophys. J. 56, 869-876] we have shown that translational diffusion studies using fluorescence recovery after photobleaching (FRAP) provide information concerning domain structures and fluid-phase connectivity in lipid bilayers in which solid and fluid phases coexist. In the present paper, translational diffusion of the fluid-phase-soluble, solid-phase-insoluble fluorescent lipid derivative N-(7-nitrobenzoxa-2,3-diazol-4-yl) dilauroyl-phosphatidylethanolamine and the fluid-phase connectivity are examined in lipid bilayers prepared from binary mixtures of 1-docosanoyl-2-dodecanoylphosphatidylcholine (C22:0C12:0PC) and 1,2-diheptadecanoylphosphatidylcholine (di-C17:0PC) by using FRAP. The phosphatidylcholine mixture used provides a eutectic system with a eutectic point at a composition of about 0.4 mole fraction of di-C17:0PC and a temperature of about 37 degrees C [Sisk, R.B., Wang, Z.Q., Lin, H.N., & Huang, C.H. (1990) Biophys. J. 58, 777-783]. Two regions in temperature and composition, respectively below and above 0.4 mole fraction of di-C17:0PC, where fluid and solid phases coexist in the same lipid bilayer, are available for examination of fluid-phase connectivity. In mixtures containing less than 0.4 mole fraction of di-C17:0PC the fluid phase coexists with a mixed interdigitated Lc gel phase composed mostly of C22:0C12:0PC, whereas in mixtures containing greater than 0.4 mole fraction of di-C17:0PC the fluid phase coexists with a P beta' gel phase mostly composed of di-C17:0PC. When the solid phase is a P beta' gel phase, the temperature of fluid-phase connectivity for the mixtures lies close to the fluidus, which means that a small (approximately 20%) mass fraction of solid phase can divide the large bulk of the bilayer that is fluid into nonconnected domains.(ABSTRACT TRUNCATED AT 250 WORDS)

Diffusion↗

PubMed1995

Dual-phase helical CT of the liver: value of arterial phase scans in the detection of small (< or = 1.5 cm) malignant hepatic neoplasms.

OBJECTIVE: Helical CT scanners now allow sequential arterial phase and portal venous phase scans of the entire liver to be obtained during a single bolus injection of contrast material. The purpose of this study was to determine if arterial phase scans improve detection of small (< or = 1.5 cm) malignant hepatic neoplasms when compared with portal venous scans alone. MATERIALS AND METHODS: Dual-phase helical CT of the liver was done in 96 patients referred for known or suspected malignant hepatic lesions. Malignant hepatic neoplasms were detected in 38 patients (27 with at least one small neoplasm), one patient had undetected metastases, one patient had a benign hepatic neoplasm, and 56 patients had no hepatic neoplasm. Proof of individual neoplasms was based on biopsy results, surgical findings, or findings on other imaging studies (primarily follow-up CT). The absence of disease was established by surgical or autopsy findings, findings on subsequent imaging studies, or a combination of clinical and laboratory data. A total of 150 ml of 60% nonionic contrast material was infused at 5 ml/sec followed by sequential arterial phase and portal venous phase helical scans of the liver. Three radiologists retrospectively reviewed the scans. Individual lesions were measured and the conspicuity of each lesion on arterial phase and portal venous phase scans was compared. The percentage of patients in whom some malignant neoplasms were detected better on the arterial phase scan was calculated using categories based on lesion size and typical tumor vascularity. RESULTS: In 10 (37%) of 27 patients who had at least one small malignant neoplasm, lesions 1.5 cm or less in diameter were only visible or were more conspicuous on the arterial phase scan. No malignant neoplasms more than 1.5 cm in diameter were visible only on the arterial phase scan. In four (11%) of 38 cases, malignant neoplasms more than 1.5 cm in diameter were more conspicuous on the arterial phase scan. The arterial phase scans improved lesion conspicuity in nine (39%) of 23 patients who had typically hypervascular neoplasms, whereas lesion conspicuity was improved in three (20%) of 15 patients who had typically hypovascular neoplasms (p = .02). The arterial phase scan resulted in the false-positive detection of lesions in two (2%) of 96 cases. CONCLUSION: Arterial phase helical CT of the liver improves detection of some small, malignant hepatic neoplasms when performed in addition to portal venous scanning. The value is greatest in those patients who have hypervascular neoplasms.

Adolescent↗

PubMed1989

Different mechanisms of phase delays and phase advances of the circadian rhythm in rat pineal N-acetyltransferase activity.

The circadian rhythm in rat pineal N-acetyltransferase (NAT) activity, which drives the rhythm in melatonin production, is controlled by a pacemaker located in the suprachiasmatic nucleus of the hypothalamus. As the NAT rhythm has two well-defined phase markers--namely, the time of the evening activity rise and of the morning decline--it is suitable for studies of the entrainment of the pacemaker by environmental light. Phase delays of the NAT rhythm proceed more rapidly than phase advances. One day after a brief light pulse applied before midnight, or after a delay in evening lights-off, or a delay of a light-dark (LD) cycle, phase delays of the evening NAT rise result in almost corresponding delays of the morning NAT decline. Consequently, the NAT rhythm is phase-shifted, but its pattern does not change. One day after a brief light pulse applied past midnight, or after bringing forward morning lights-on, or after an advance of an LD cycle, the morning NAT decline is phase-advanced, but the evening rise is not phase-advanced at all or may even by phase-delayed. Consequently, the phase relationship between the evening NAT activity onset and the morning offset may be compressed considerably, and it may take several transient cycles before phase advances of the morning NAT decline are followed by corresponding advances of the evening NAT rise. Due to the phase-delaying effect of evening light on the NAT rise and to the phase-advancing effect of morning light on the NAT decline, the phase relationship between the NAT rise and the decline is compressed on long days and decompressed on short days. Different phase shifts of the evening NAT rise and of the morning decline, even in opposite directions, are consistent with the hypothesis of a complex, two-component (evening-morning, or E-M) pacemaker controlling the NAT rhythm. As the E-M phase relationship determines duration of the high night melatonin production, and the duration of the nocturnal melatonin pulse may convey information on daylength, the data are consistent with the internal coincidence model for photoperiodic time measurement.

Animals↗

PubMed1995

Phase-dependent phase shift of methamphetamine-induced circadian rhythm by haloperidol in SCN-lesioned rats.

Haloperidol, a non-selective dopamine receptor antagonist, was injected intraperitoneally in to suprachiasmatic nucleus (SCN)-lesioned rats at various phases of the locomotor activity rhythm induced by methamphetamine (MAP) treatment. A single injection of haloperidol shifted the phase of MAP-induced locomotor rhythm phase dependently, while saline injection had no effect on the phase. A phase-response curve of MAP-induced rhythm for haloperidol had a small phase-advancing area at CT 13 to 15, a large phase-delaying area at CT 3 to 7 and a dead zone at CT 17 to 1. Although the day-to-day variation of MAP-induced locomotor rhythm was about 2.5-times as great as that of light entrainable circadian rhythm, the phase shifts of both directions were statistically significant. Phase delay shifts at CT 5 depended on the dose of haloperidol. In addition to the phase-shifting effect, haloperidol suppressed the MAP-induced locomotor activity for activity for about 10 h regardless of the phase of the injection. Pentobarbital also suppressed ther locomotor activity for a similar duration. However, significant phase shift was not detected with pentobarbital injected at CT 5 or CT 13, at the phase where haloperidol induced the maximal phase delay or advance, respectively. Present findings suggest that the dopaminergic mechanism is involved in the entrainment and/or oscillatory mechanism of the MAP-induced rhythm.

Animals↗

PubMed1996

Ucon-benzoyl dextran aqueous two-phase systems: protein purification with phase component recycling.

Benzoyl dextran with a degree of substitution of 0.18 was synthesized by reacting dextran T500 with benzoyl chloride. A new type of aqueous two-phase system composed of benzoyl dextran as bottom phase polymer and the random copolymer of ethylene oxide and propylene oxide (Ucon 50-HB-5100) as top phase polymer has been formed. The phase diagram for the system Ucon 50-HB-5100-benzoyl dextran with a degree of substitution of 0.18 was determined at room temperature. This two-phase system has been used to purify 3-phosphoglycerate kinase from baker's yeast. The top-phase polymer (Ucon) can be separated from target enzyme by increasing the temperature. The bottom-phase polymer (benzoyl dextran) could be recovered by addition of salt. Yeast homogenate was partitioned in a primary Ucon 50-HB-5100-benzoyl dextran aqueous two-phase system. After phase separation the top phase was removed and temperature-induced phase separation was used for formation of a water phase and a Ucon-rich phase. The benzoyl dextran-enriched bottom phase from the primary system was diluted, and the polymer was separated from water by addition of Na2SO4.

Dextrans↗

PubMed1997

Phosphatidylcholine-fatty acid membranes: effects of headgroup hydration on the phase behaviour and structural parameters of the gel and inverse hexagonal (H(II)) phases.

The phase behaviour and structural parameters of a homologous series of saturated diacyl phosphatidylcholine/fatty acid 1:2 (mol/mol) mixtures having chain lengths from C12 to C20 were studied by X-ray diffraction and calorimetry, as a function of water content. The chain-melting transition temperatures of the 1:2 PC/FA mixtures are found to be largely independent of the degree of hydration. For all chain lengths, the tilted L(beta') and rippled P(beta') gel phases of the pure PC component are replaced by an untilted L(beta) gel phase in the 1:2 PC/FA mixtures. This gel phase swells considerably upon hydration, with a limiting water layer thickness in the range 18-24 A, depending on the chain length. However, unlike pure phospholipid systems, the lateral chain packing within the gel phase bilayers is essentially identical in both the dry and the fully hydrated states. The fluid bilayer L(alpha) phase is suppressed in the 1:2 mixtures, being replaced by inverse non-lamellar phases for all chain lengths greater than C12, and at all levels of hydration. For chain lengths of C16 and greater, the inverse hexagonal H(II) phase is formed directly upon chain melting, at all water contents. For the shorter chain length mixtures, the behaviour is more complex, with the H(II) phase forming at low hydration, but with bicontinuous cubic phases appearing at higher levels of hydration. The implications of these surprising results are explored, in terms of the effective hydrophilicity of the associated PC and FA headgroups and the packing within the interfacial region. We suggest that the presence of the fatty acids significantly alters the lateral stress profile across the lipid monolayer in the fluid state, compared to that of the corresponding pure PC system, such that inverse phases, where the interface bends towards the water, become strongly favoured. Furthermore, for short chain lengths, packing constraints favour the formation of phases with negative interfacial Gaussian curvature, such as the bicontinuous cubic phases, rather than the H(II) phase, which has more severe chain packing frustration.

Calorimetry↗

PubMed1998

On the kinetics of phase separation in aqueous two-phase systems.

The effect of the tie-line location (phase volume ratio) on the kinetics of phase separation in batch PEG/salt aqueous two-phase systems (ATPS) has been investigated. PEG/sulphate systems with a stability ratio (sr) of 0.34 and 0.37 and relative tie-line lengths in the range 0.1 to 0.6 for a continuous top phase and in the range 0.03 to 0.15 for a continuous bottom phase were used in the batch studies. A continuous settler was designed with three different inlet geometries. Phase separation is much faster when the bottom phase is continuous and in this case the location on the tie-line and the presence or absence of Bacillus subtilis extract makes little difference. When the top phase is continuous the relative sizes of the phases (phase ratio, R. relative distance on tie-line, rd) has an important effect, the larger the top phase (larger R and rd) the slower the phase separation. The presence of Bacillus extract also makes the operation slower which is more marked at the largest values of R (and rd). At the largest volume ratios (R or rd) three different settling regions have been recognised, a region of coalescence, a region of drops moving to the interphase and a region where drops queue at the interphase to coalesce into the large phase. A modified correlation that takes into account the location on the tie-line and thus volume ratio (R) and relative distance (rd) has been proposed and successfully tested. The behavior of batch and continuous systems in the presence and absence of Bacillus subtilis extract in systems with continuous bottom phase was also studied. The settling velocity was lower in the continuous than in the batch systems, and in both cases the initial rate was lower in the presence of Bacillus extract.

Bacillus subtilis↗

PubMed1994

Detection of coexisting fluid phospholipid phases by equilibrium Ca2+ binding: peptide-poor L alpha and peptide-rich HII phase coexistence in gramicidin A'/phospholipid dispersions.

The isothermal phase behavior of three gramicidin A'/phospholipid mixtures was investigated by an equilibrium Ca(2+)-binding technique. The phospholipid component was 1,2-dioleoyl-sn-glycero-3-phosphoserine (DOPS), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoserine (POPS), or POPS/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) at a constant mole ratio of 1/4. The bulk aqueous free Ca2+ concentration, [Ca2+]*f, in equilibrium with one or two gramicidin A'/phospholipid fluid phases and a small amount of the Ca (phosphatidylserine)2 gel phase, was measured as a function of composition at 20 degrees C by use of chromophoric high-affinity Ca2+ chelators. The coexistence of two gramicidin A'/phospholipid fluid phases was detected by an invariance in [Ca2+]*f over the range of compositions throughout which the two phases coexist. The compositions of the two coexisting phases are determined by the compositions at which the invariance in [Ca2+]*f begins and ends. With each of the gramicidin A'/phospholipid mixtures, we estimate that the composition of the gramicidin-poor phase is 0.03-0.04 mole fraction gramicidin A' and the composition of the gramicidin-rich phase is 0.13-0.14 mole fraction gramicidin A'. Characterization of these phases by low-angle X-ray diffraction revealed that, in each case, the gramicidin-poor phase is an L alpha phase and the gramicidin-rich phase is an HII phase. The isothermal phase behavior of gramicidin A'/POPC mixtures at approximately 23 degrees C, as determined by low-angle X-ray diffraction, was found to be similar to that of the other gramicidin A'/phospholipid mixtures.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding Sites↗

PubMed1996

Biochemical changes in three-day-event horses at the beginning, middle and end of Phase C and after Phase D.

Blood samples were collected 12-16 h before the Speed and Endurance test, immediately after steeplechase, midway through Phase C (4 km marker), at the end of Phase C and immediately after cross-country from 36 horses that completed a 3-day-event at the CCI* (n = 19) or CCI** (n = 17) level. Packed cell volume (PCV), plasma concentrations of sodium, potassium, chloride, ionized calcium, pH and lactate; and serum concentrations of total protein (TP), albumin, total calcium, alkaline phosphatase (AP), gamma glutamyl transferase (GGT), creatine kinase (CK), aspartate aminotransferase (AST), glucose and creatinine were measured. No differences were noted in any biochemical measurements between the CCI* and CCI** horses at any sampling time, despite differences in speed and length of various phases of the Speed and Endurance test. For all horses (n = 36), biochemical parameters changed significantly over time (P < 0.01). The PCV, calcium, potassium, lactate, total protein and albumin concentrations were significantly increased over pre-exercise concentrations immediately after Phase B. During Phase C, these parameters decreased towards pre-exercise concentrations, thereby supporting the concept that Phase C is a recovery phase. In contrast, chloride concentration decreased, and the creatinine concentration and CK increased compared to pre-exercise concentrations from the end of Phase B to the end of Phase C. These changes probably resulted from fluid and electrolyte losses in sweat, reduced renal blood flow and continued muscular activity. Many parameters did not change significantly between the 4 km marker (midway point on Phase C) and the end of Phase C. However, there were a few notable exceptions: potassium, chloride, lactate and glucose concentrations decreased, whereas pH and creatinine concentrations increased significantly from the 4 km marker to the end of Phase C. The most significant benefit of the extra distance from the 4 km marker to the end of Phase C was that it facilitated further dissipation of lactate concentrations prior to the start of Phase D.

Alkaline Phosphatase↗

PubMed1995

Using a phase-locked mutant of Myxococcus xanthus to study the role of phase variation in development.

The bacterium Myxococcus xanthus undergoes a primitive developmental cycle in response to nutrient deprivation. The cells aggregate to form fruiting bodies in which a portion of the cells differentiate into environmentally resistant myxospores. During the growth portion of the M. xanthus life cycle, the organism also undergoes a phase variation, in which cells alternate between yellow and tan colony-forming variants. Phase variation occurs in our laboratory strain (M102, a derivative of DK1622) at a frequency high enough that a single colony of either the yellow or the tan phase already contains cells of the alternate phase. In this study we demonstrate that tan cells within a predominantly yellow population of phase variation-proficient cells are preferentially recovered as heat- and sonication-resistant spores. To further investigate the possibility of a differential role of tan and yellow cells during development, a tan-phase-locked mutant was used to compare the developmental phenotypes of a pure tan population with a predominantly yellow, phase variation-proficient population. Pure tan-phase populations did not produce fruiting bodies or mature spores under conditions in which predominantly yellow wild-type populations did so efficiently. Pure populations of tan-phase cells responded to developmental induction by changing from vegetative rod-shaped cells to round forms but were unable to complete the maturation to heat- and sonication-resistant, refractile spores. The developmental defect of a tan-phase-locked mutant was rescued by the addition of phase variation-proficient cells from a predominantly yellow culture. In such mixtures the tan-phase-locked mutant not only completed the process of forming spores but also was again preferentially represented among the viable spores. These findings suggest the intriguing possibility that the tan-phase cells within the vegetative population entering development are the progenitors of spores and implicate a requirement for yellow-phase cells in spore maturation.

Bacterial Adhesion↗

PubMed1999

Pancreatic-phase versus portal vein-phase helical CT of the pancreas: optimal temporal window for evaluation of pancreatic adenocarcinoma.

OBJECTIVE: Our objective was to use helical CT to compare the enhancement attenuation values of pancreatic adenocarcinoma, adjacent normal pancreas, and critical vascular structures during the pancreatic phase and portal vein phase. SUBJECTS AND METHODS: Forty-one patients with pathologically proven pancreatic adenocarcinoma underwent dual-phase thin-section dynamic helical CT using a pancreatic-phase and portal vein-phase protocol. The scan delay after initiation of the contrast bolus was 40 sec for the pancreatic phase and 70 sec for the portal vein phase. Attenuation values after i.v. contrast administration were calculated during both phases of scanning for normal pancreas, pancreatic tumor, celiac axis, superior mesenteric artery, superior mesenteric vein, splenic vein, and portal vein. Quantitative values were assessed using regions of interest. RESULTS: Mean differences of enhancement between tumor and normal pancreas were significantly greater in the pancreatic phase (57 H) than the portal vein phase (35 H) (p = .0001). Enhancement values of all the critical vascular structures were also significantly greater in the pancreatic phase than the portal vein phase (p < .001). CONCLUSION: With dynamic thin-section helical CT, pancreatic-phase scanning provides greater differences in contrast enhancement between normal pancreas and pancreatic tumor and between pancreatic tumors and surrounding critical vascular structures than does portal vein-phase scanning.

Adenocarcinoma↗

PubMed1978

[The 3 phases of schizophrenic psychosis and their phase-specific psychotherapy].

It is not the diagnostic evaluation but merely the phase in which we find our patient, that determines about the process of psychotherapy with schizophrenic patients. There are three phases--or, more approximately, four phases (phase one to three plus "phase zero")--to be differentiated: Phase Zero: This phase precedes an obvious clinical appearance of psychosis. Patients feel ridiculous in their anxiety and are not yet capable to create the symptomatology of psychosis.--Intensive participation in those strange perceptions and the attempt to witness the same experiences as the patient does, often help to prevent the formation of a severe psychosis. Phase One: Deep psychosis with common symptomatology. Verbal communication in the usual form is no more possible. Only answering the patient in his own language--speaking as he speaks and behaving as he does--helps to overcome his permanent isolation. Phase Two: Stage where the patient leaves his psychotic world and does not yet live in the world of his "healthy" surroundings.--In this phase psychotherapy intends to lead towards a confrontation with the previous psychotic experiences in order to integrate them into his personality. Phase Three: Phase of return towards a more adequate behaviour.--In this phase the therapist helps his patient to build up his "narcissistic coat" in order to create a shelter, where he can retreat; out of this "cocoon" he is able to observe what happens around him, without being thrown back into a severe psychotic crisis. On the other hand there may arise situations of "relapses" (so-called intermediary stages). These phases, which resemble common depression, can be understood as substitutes of the former psychotic situation. It is insight in its uttermost distinction that leads to secondary stages. Therefore psychotherapy will be most helpful, when the understanding of the circumstances that lead to such situations, is not evaded but promoted; the more intensely these promotions, the better the prognosis.

Humans↗

PubMed1990

Polymorphism of a lipid extract from Pseudomonas fluorescens: structure analysis of a hexagonal phase and of a novel cubic phase of extinction symbol Fd--.

The phase diagram of the Pseudomonas fluorescens lipid extract is unusual, in the sense that it displays a cubic phase straddled by a hexagonal phase. The hexagonal phase was studied over an extended concentration range, and the reflections were phased on the assumption that the structure contains circular cylinders of known radius. The cubic phase, whose extinction symbol is Fd--, was analyzed by reference to space group No. 227 (Fd3m). The phases of the reflections were determined by using a novel pattern recognition approach, based upon the notion that the average fourth power of the electron density contrast mean value of (delta r)4 is dependent on chemical composition but not on physical structure, provided that the function delta r(r) satisfies the constraints mean value of (delta r) = 0 and mean value of (delta r)2 = 1. As a further constraint, a shape normalization is used, in the form of a Gaussian apodization of the intensities, which has the effect of normalizing the curvature of the autocorrelation function at the origin. We analyzed two cubic samples of different composition: for each of them we generated all the phase combinations compatible with the X-ray scattering data and we searched for those whose mean value of (delta r)4 best agrees with the hexagonal phase. Taking advantage of the favorable properties of the phase diagram, we carefully explored the effects of various parameters; we concluded that the chemical composition of the phases being compared must be identical, that the X-ray scattering data should not be truncated artificially, and that the apodization must be mild so that the curvature takes a value intermediate between those corresponding to the raw data of the two phases. When all these precautions were taken, mean value of (delta r)4 was found to be remarkably invariant; this conclusion is important in view of the possible usefulness of the novel technique in tackling ab initio--and at very low resolution--structural problems of more general interest. The structure of the cubic phase consists of a 3D network of rods joined tetrahedrally 4 by 4 according to a diamond lattice and of a family of quasi-spherical disjointed micelles; the core of the rods and of the micelles is polar, and the interstices are filled by the hydrocarbon chains (structure of type II). All the dimensions (diameter of rods and micelles, area per chain at the polar/apolar interface) are consistent with the chemical properties of the system.(ABSTRACT TRUNCATED AT 400 WORDS)

Lipids↗

PubMed1997

Comparison of DNA bending by Fos-Jun and phased A tracts by multifactorial phasing analysis.

Studies of DNA bending by Fos and Jun using different methods have yielded contradictory results. Whereas gel electrophoretic phasing analysis indicates that Fos and Jun bend DNA, results obtained through X-ray crystallography and ligase-catalyzed cyclization suggest that they do not. To test the assumptions underlying phasing analysis and to examine DNA bending by Fos and Jun, a multifactorial phasing analysis approach based on the distinct electrophoretic mobilities of DNA fragments of diverse shapes was developed. In this approach, the spacing between the bends, the length of sequences flanking the bends, and the acrylamide concentration in the gel are varied. Two closely spaced intrinsic bends with long flanking sequences had the same effect on electrophoretic mobility as a single bend corresponding to the sum of the bends when they were arranged in phase, and the difference between the bends when they were arranged out of phase. Based on the phase-dependent electrophoretic mobility variation of fragments containing intrinsic DNA bends of different magnitudes, three criteria for determination whether the phase-dependent mobility variation of protein-DNA complexes is caused by DNA bending were adopted. Complexes formed by the bZIP domains of Fos and Jun fulfilled each of these criteria. First, the electrophoretic mobility variation induced by Fos and Jun was proportional to that caused by an intrinsic bend over a broad range of acrylamide concentrations. Second, the mobility difference between fragments containing in phase and out of phase bends was reduced by an increase in the separation between the bends. The separation between the bends had the same effect on the electrophoretic mobility variation caused by Fos and Jun as well as intrinsic bends on long DNA fragments at low acrylamide concentrations. Third, on short DNA fragments analyzed at high acrylamide concentrations, two intrinsic bends separated by long spacers caused a larger decrease in electrophoretic mobility when they were out of phase than when they were in phase. This reversal of the phase dependence of the electrophoretic mobility variation was also observed for complexes formed by truncated Fos and Jun. Thus, the phase-dependent mobility variation of Fos and Jun complexes is due to DNA bending.

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