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At least 145 records · Page 8Linked to original sources

PubMed1989

D-ribulose-1,5-bisphosphate carboxylase/oxygenase: function-dependent structural changes.

The key carboxylating enzyme of the reductive pentose phosphate cycle, D-ribulose-1,5-bisphosphate carboxylase/oxygenase [RuBisCO] isolated from the chemolithoautotrophic, H2-oxidizing bacterium Alcaligenes eutrophus H16 has been analyzed by several different techniques that allow conclusions about structure and function-dependent structural changes. The techniques include a novel approach in which the enzyme was induced to form 2D-crystals suitable for electron microscopy in each of its three stable functional states: as active enzyme [Ea] (in the presence of Mg2+ and HCO3-); as inactivated enzyme [Eia] (in the absence of Mg2+ and HCO3-) and as enzyme locked in an in vitro transition state [CABP-E] (Ea fully saturated with the transition state analogue 2-carboxy-D-arabinitol-1,5-bisphosphate [CABP-E]). In conjunction with X-ray crystallography, X-ray small angle scattering and other biophysical and biochemical data, the results obtained by electron microscopy support the idea that drastic configurational changes occur. Upon transition from Ea to the CABP-E the upper and lower L4S4 halves of the molecule consisting of eight large and eight small subunits (L8S8; MW = 536,000 Da) are assumed to be laterally shifted by as much as 3.6 nm relative to one another while the location of the small subunits on top of the large subunits, and relative to them, remains the same. For the Eia a similar sliding-layer configurational change in the range of 2-2.5 nm is proposed and in addition it is suggested that other configurational/conformational changes take place. The proposed structural changes are discussed with respect to the current model for the tobacco enzyme and correlated with data obtained for various other plant and (cyano) bacterial L8S8 RuBisCOs leading to speculations about structure-function relationships.

Microscopy, Electron↗

PubMed1985

Control of cell differentiation during proliferation. II. Myeloid differentiation and cell cycle arrest of HL-60 promyelocytes preceded by nuclear structural changes.

The time-dependent dynamics of nuclear structure, cell cycle transit and arrest, and cellular differentiation were studied using the human promyelocytic leukemia cell line HL-60. Myeloid differentiation of HL-60 cells was induced by 10(-6) M beta, all trans, retinoic acid (RA). During exponential growth the cells had G1, S, G2 and M durations of 9, 11, 0.5 and 0.5 h respectively. Significant growth arrest in the G1/0 phase of the cell cycle was apparent after 48 h of RA exposure or after two division cycles. Thereafter, cells arrested in G1/0 with wide dispersion in times of arrest which extended over several cell cycle generation times. The kinetics of phenotypic differentiation, detected by phorbol myristate acetate inducible superoxide production, paralleled those of G1/0 growth arrest with similar lag and dispersion. These kinetics are consistent with a model hypothesizing the existence of an S-phase differentiation control (DC) point regulating both terminal proliferation and differentiation. Before any cell differentiation or termination of cell proliferation occurred, the nuclei of RA-treated cells underwent a structural change detected by narrow-angle light scatter measured with flow cytometry. Narrow-angle light scatter was transiently reduced, reaching a nadir at 24-48 h and returning to control values at 96 h. This change was independent of cell cycle phase or total nuclear protein content. It was associated with a morphological change of the nuclear membrane from a smooth to dimpled or pitted structure. These findings focus attention on the potential significance of nuclear structural reorganization as an early event during cell differentiation.

Cell Cycle↗

PubMed1995

Unlike the quaternary structure transition, the tertiary structure change of the 240s loop in allosteric aspartate transcarbamylase requires active site saturation by substrate for completion.

The quaternary structural change associated with the homotropic cooperative interactions in Escherichia coli aspartate transcarbamylase (ATCase) is accompanied by various tertiary structural modifications; the most notable one involves the 240s loop formed by residues 230--245 of the catalytic chain. In order to monitor local conformational changes in this region by fluorescence spectroscopy, Tyr-240 has been replaced by a Trp residue, in a mutant enzyme, in which both naturally occurring Trp residues in positions 209 and 284 of the catalytic chains had previously been substituted by Phe residues. This F209F284W240-ATCase still displays homotropic cooperativity for aspartate and undergoes the same T to R quaternary structure change as does the wild-type enzyme. Upon binding of the bisubstrate analogue N-(phosphonoacetyl)-L-aspartate, the fluorescence emission spectrum of this mutant shows a red shift directly proportional to the fraction of catalytic sites occupied by this compound, a maximum value of 4 nm being attained when all six active sites are ligated. An identical shift is observed with the catalytic subunits of this modified enzyme, when all three active sites are occupied. In contrast, the quaternary structural change of the F209F284W240-ATCase, monitored by small-angle X-ray scattering, is complete when only four out of six catalytic sites are occupied. Thus, the 240s loop adopts its final conformation only when the neighboring active site is bound.

Allosteric Site↗

PubMed1995

Role of hyperphagia in structural changes of small intestine during lactation.

The present study was conducted to investigate the cause of the structural changes of small intestine during lactation in albino rats. Anatomical measurements (total length, total wet weight and total dry weight) and histological studies of small intestine were undertaken in virgin control rats, lactating control rats, lactating rats with restricted food intake and lactating rats with restricted litter size. Restriction of food intake prevented the growth of small intestine during lactation, while restriction of litter size had no effect. Results indicate that the structural changes in small intestine are due to work hypertrophy secondary to hyperphagia and not due to any hormonal factors.

Animals↗

PubMed1992

Ca(2+)-dependence of structural changes in troponin-C in demembranated fibers of rabbit psoas muscle.

The Ca(2+)-dependence of structural changes in troponin-C (TnC) has been detected by monitoring the fluorescence from TnC labeled at Methionine-25, in the NH2-terminal domain, with danzylaziridine (TnC-DANZ) and then exchanged for endogenous TnC in glycerinated single fibers. The fluorescence-pCa relation obtained from fibers stretched to a sarcomere length greater than 4.0 microns evidenced two transitions: a small one, attributable to the binding of Ca2+ to the high affinity, Ca(2+)-Mg(2+)-binding sites of TnC; and a large one, attributable to the binding of Ca2+ to the low affinity, Ca(2+)-specific binding sites of TnC. In the fluorescence-pCa relation determined with fibers set to a sarcomere length of 2.4 microns, hence obtained in the presence of cycling cross-bridges, the large transition had the same Ca(2+)-dependence as did the development of tension. These results indicate that the NH2-terminal globular domain of TnC is modified by the binding of Ca2+ to sites located in both globular domains and that the structural changes in TnC resulting from the binding of Ca2+ to the low-affinity sites, but not to the high-affinity sites, are directly associated with the triggering of contraction.

Adenosine Triphosphate↗

PubMed1987

The effects of protein synthesis inhibition on structural changes associated with learning in the chick.

The effect of the protein synthesis inhibitor anisomycin on the structural changes associated with passive avoidance learning in the chick was investigated. Chicks were trained when they were 24 h old by allowing them to peck at a shiny bead coated with either water or the aversive-tasting substance methylanthranilate (MeA). Chicks which peck the MeA-coated bead will on subsequent testing avoid pecking a similar, but water-coated bead. Behavioural testing was carried out 12 h after training and immediately afterwards the chicks were killed and their brains prepared for electron microscopy. A specific region of the forebrain, the intermediate and medial part of the hyperstriatum ventrale (IMHV) was investigated. When the IMHV of the MeA trained chicks was compared with that of water-trained controls structural changes of the synapse were detected. These changes involved a significant increase in the mean length of the postsynaptic density (LPSD) of symmetrical synapses in the left IMHV. Chicks injected with 0.8 mg of anisomycin 30 min before training with a MeA-coated bead showed aversion for the shiny bead when tested 12 h later. Electron microscopic analysis of the IMHV from these amnestic chicks showed no evidence for the change in LPSD demonstrated in the water-injected controls. These results are discussed in relation to the nature of the memory trace induced by training on a passive avoidance task.

Animals↗

PubMed1982

Structural changes in the canine lung and pulmonary arteries after pneumonectomy.

The study set out to describe the structural changes in the remaining lung of beagle dogs after left-sided pneumonectomy, performed at 6-10 wk or 1 yr of age. After a 5-yr postoperative recovery, lung volume and weight had increased in the operated groups, though only the latter was significant in comparison with 5-yr-old controls. In both operated groups, total alveolar number in the right lung was normal. The total volume of alveolar ducts, mean linear intercept, and (in the young operated group) mean alveolar volume were increased, indicating a compensatory enlargement of distal air spaces. Lobar differences reinforced these conclusions. In the 1-yr operated group, medial hypertrophy was present in preacinar arteries, with a similar trend in intra-acinar arteries where peripheral extension of medial smooth muscle was also present. Despite the lack of structural change in their pulmonary arterial system, the young operated group had right ventricular hypertrophy. Previously reported evidence of alveolar proliferation shortly after pneumonectomy probably represents a speeding up of normal developmental patterns, but after prolonged recovery the final alveolar number is no greater than normal.

Animals↗

PubMed1986

Immunohistochemical studies on structural changes of the hepatic lobules in chronic liver diseases.

Liver biopsy specimens were examined immunohistochemically to clarify structural changes of the hepatic lobules in chronic liver diseases. In normal liver carbohydrate antigen 19-9 was located in the biliary ductular epithelium, whereas factor VIII-related antigen was observed in the endothelium of portal veins, hepatic arteries, and central veins. This antigen was not detected in the sinusoidal endothelium. In contrasts, monoclonal antibody OKM5 was reactive with the sinusoidal endothelium but was unreactive with the endothelium of the portal blood vessels or central veins. In chronic active hepatitis and liver cirrhosis, both carbohydrate antigen 19-9 positive biliary ductular cells and factor VIII-related antigen positive endothelial cells were not only observed in the enlarged portal area but also extended into the parenchyma. They were occasionally accompanied by fibers. These findings suggest that fibrosis, ductular epithelial, and blood vascular proliferation in the portal space and their invasion into the parenchyma might gradually cause structural changes of the hepatic lobules in chronic liver disease.

Antigens↗

PubMed1989

Structure-activity relationship between prostacyclin and its platelet receptor. Correlation of structure change and the platelet activity.

Correlation analysis between the structural changes of PGI2 and the corresponding changes in platelet activity was performed to look into the following structural features: (1) the spatial relationship of critical functional groups, (2) conformational flexibility of the molecule as a result of chemical modification; (3) charge distribution around C6a; (4) hydrogen-bonding capability and mispairing and (5) the steric effects which resulted from chemical modifications. Our studies led to three important conclusions: (1) The C1 carboxylate and C11, C15 hydroxyl groups of PGI2 are essential for platelet activity. Modifications that change their relative positions reduce the activity. The ring structure and the C5 and C13 double bonds are molecular designs to maintain this unique geometry. (2) The C6a oxygen, although not vital to the binding geometry, is important for the biological potency. Decreasing the electronegativity of C6a oxygen leads to decreased potency. (3) We propose that any additional hydrogen-bond donor present between C1 and C15 could cause a hydrogen-bond mispairing and therefore a decreased activity. These findings should be useful for designing new PGI2 analogues and for determining the configuration of receptor-associated PGI2 by a molecular mechanics technique.

Animals↗

PubMed1999

Temperature jump-induced secondary structural change of the membrane protein bacteriorhodopsin in the premelting temperature region: a nanosecond time-resolved Fourier transform infrared study.

The secondary structural changes of the membrane protein, bacteriorhodopsin, are studied during the premelting reversible transition by using laser-induced temperature jump technique and nanosecond time-resolved Fourier transform infrared spectroscopy. The helical structural changes are triggered by using a 15 degrees C temperature jump induced from a preheated bacteriorhodopsin in D2O solution at a temperature of 72 degrees C. The structural transition from alphaII- to alphaI-helices is observed by following the change in the frequency of the amide I band from 1667 to 1651 cm-1 and the shift in the frequency of the amide II vibration from 1542 cm-1 to 1436 cm-1 upon H/D exchange. It is found that although the amide I band changes its frequency on a time scale of <100 ns, the H/D exchange shifts the frequency of the amide II band and causes a complex changes in the 1651-1600 cm-1 and 1530-1430 cm-1 frequency region on a longer time scale (>300 ns). Our result suggests that in this "premelting transition" temperature region of bacteriorhodopsin, an intrahelical conformation conversion of the alphaII to alphaI leads to the exposure of the hydrophobic region of the protein to the aqueous medium.

Bacteriorhodopsins↗

PubMed1999

Structural changes of hake (Merluccius merluccius L.) fillets: effects of freezing and frozen storage.

Structural changes in hake (Merluccius merluccius L.) fillets as affected by freezing method and frozen storage temperature have been studied through Raman spectroscopy and related to changes in texture and functionality. Changes in protein secondary structure were observed due to storage temperature, accompanied by changes in apparent viscosity and shear resistance. Samples at -10 degrees C showed greater structural alteration than at -30 degrees C in terms of increase of beta-sheets at the expense of alpha-helices. An increase of unordered protein structure was found only in samples stored at -10 degrees C. Exposure of buried tryptophan residues was observed at both storage temperatures. The decrease of the deltaCH(2) band upon storage suggested an increase of hydrophobic interactions of aliphatic residues. Except for liquid air frozen fillets, all samples showed a decrease of the nuO-H/nuC-H band ratio compared to the fresh ones, this decrease being higher the harsher the conditions.

Animals↗

PubMed1989

Structural changes in the tracheae of preterm lambs induced by ventilation.

Compliant immature airways sustain significant deformation following positive pressure ventilation. To evaluate the structural changes induced by in vivo positive pressure ventilation, tracheae of preterm lambs (107-116 d gestational age) were studied histologically. Nonventilated (group I: n = 7) and ventilated (group II: n = 7) tracheal segments were excised and studied by histologic and morphometric techniques. Computerized image analysis was used to measure dimensions of tracheal wall components and of the tracheal section. The circumference, diameter, and cross-sectional area of the section as well as the length of the trachealis muscle were significantly greater; although the thickness of the muscle and cartilage were seen to be significantly lower in group II sections compared to group I sections. Also, in comparison to group I, in group II sections there was lesser overlap of the posterior free ends of tracheal cartilage and the epithelial layer was flattened and focally abraded. Our findings demonstrate structural changes in the airway of preterm animals and characterize alterations in the geometric arrangement of muscle and cartilage after PPV. These results suggest possible structural mechanisms for the functional changes seen during and subsequent to mechanical ventilation.

Animals↗

PubMed1999

Protonation state and structural changes of the tetrapyrrole chromophore during the Pr --> Pfr phototransformation of phytochrome: a resonance Raman spectroscopic study.

The photoconversion of phytochrome (phytochrome A from Avena satina) from the inactive (Pr) to the physiologically active form (Pfr) was studied by near-infrared Fourier transform resonance Raman spectroscopy at cryogenic temperatures, which allow us to trap the intermediate states. Nondeuterated and deuterated buffer solutions were used to determine the effect of H/D exchange on the resonance Raman spectra. For the first time, reliable spectra of the "bleached" intermediates meta-R(A) and meta-R(C) were obtained. The vibrational bands in the region 1300-1700 cm(-)(1), which is particularly indicative of structural changes in tetrapyrroles, were assigned on the basis of recent calculations of the Raman spectra of the chromophore in C-phycocyanin and model compounds [Kneip, C., Hildebrandt, P., Németh, K., Mark, F., Schaffner, K. (1999) Chem. Phys. Lett. 311, 479-485]. The experimental resonance Raman spectra Pr are compatible with the Raman spectra calculated for the protonated ZZZasa configuration, which hence is suggested to be the chromophore structure in this parent state of phytochrome. Furthermore, marker bands could be identified that are of high diagnostic value for monitoring structural changes in individual parts of the chromophore. Specifically, it could be shown that not only in the parent states Pr and Pfr but also in all intermediates the chromophore is protonated at the pyrroleninic nitrogen. The spectral changes observed for lumi-R confirm the view that the photoreaction of Pr is a Z --> E isomerization of the CD methine bridge. The subsequent thermal decay reaction to meta-R(A) includes relaxations of the CD methine bridge double bond, whereas the formation of meta-R(C) is accompanied by structural adaptations of the pyrrole rings B and C in the protein pocket. The far-reaching similarities between the chromophores of meta-R(A) and Pfr suggest that in the step meta-R(A) --> Pfr the ultimate structural changes of the protein matrix occur.

Avena↗

PubMed1997

Structural changes in the gastric foveolar epithelium in Helicobacter pylori-positive gastritis revealed by keratin immunohistochemistry.

To clarify structural changes in the gastric foveolar epithelium in Helicobacter pylori (Hp)-positive gastritis, the expression rates of keratins 8, 18, 19, and 20 were assessed immunohistochemically in normal tissue and chronic gastritis. In normal tissue, keratin 8 was found in 100% of the cells. Staining for keratins 18 and 19 was abundantly positive. Keratin 20 was not expressed in the deep foveolae, but present in the upper foveolae and on the tips. No differences were found between the antrum and the body. In chronic gastritis, both Hp-positive and -negative, keratins 8, 18, and 19 were expressed comparably to normal tissue. Keratin 20 expression in the antrum was significantly lower in Hp-positive compared with Hp-negative gastritis (P < .05) and normal tissue (P < .05). In the body, staining for keratin 20 did not differ significantly between all groups. The difference in keratin 20 expression between the antrum and the body in Hp-positive gastritis was significant (P < .05). After successful eradication, staining for keratin 20 in the antrum normalized within 6 months (P < .05). These findings indicate structural changes in the gastric foveolar epithelium in Hp-positive gastritis. They predominantly include the antral region and show full reversibility after eradication.

Adult↗

PubMed2000

Relationship of decrease in fecundity with advancing age to structural changes in mouse endometrium.

The aim of this study was to determine whether a relationship exists between decrease in fecundity and structural changes in the antimesometrial endometrium of the mouse. Fecundity was calculated as the number of animals showing a placental sign/number of copulated animals x 100 (%). Structural changes in the endometrium were examined by electron microscopy. A negative correlation between age and fecundity was found. Fecundity was 50% at 7 mo of age. At this age, amorphous material appeared in the region between the basement membrane deep to the luminal epithelium and the subepithelial cells. This material was sometimes attached to the basement membrane. It increased in amount with advancing age, as fecundity decreased. The structure of the uterine luminal epithelial cells did not alter with age. The results indicated that decrease in fecundity with advancing age is correlated with the appearance of amorphous material beneath the basal lamina of the endometrial epithelium. It is suggested that this could impair communication between the luminal epithelium and the endometrial stroma, which plays an important role in implantation.

Aging↗

PubMed1980

Raman difference spectroscopy of tertiary and quaternary structure changes in methaemoglobins.

There have been several resonance Raman scattering investigations of the effect of inositol hexaphosphate (IHP) on methaemoglobins. In those studies the sensitivity for detecting frequency differences was limited to 1-2 cm-1, and consequently frequency differences were not detected although spectral intensity differences due to changes in spin equilibria were. Shelnutt et al. recently reported on the observation of frequency differences induced by changes in the quaternary structure of chemically modified deoxyhaemoglobins. An improved Raman difference spectroscopic technique with 0.1 cm-1 sensitivity allowed the detection of these differences. We report here the application of this technique to a series of methaemoglobins with and without the addition of IHP. In addition to the intensity changes resulting from changes in the spin equilibria, we have observed frequency differences. In all liganded methaemo-globins that we examined a decrease in frequency of the mode in the 1,370 cm-1 region was observed on addition of IHP. In those in which a quaternary structure change is known to occur the frequency difference is greater than 0.5 cm-1. In those in which no quaternary structure change occurs [metHbA(CN-) and methHbA(N-3)] the frequency difference is smaller (approximately 0.15 cm-1).

Hemoglobin A↗

PubMed1997

Influence of acid aerosol droplet size on structural changes in the rat lung caused by acute exposure to sulfuric acid and ozone.

To investigate whether aerosol droplet size influences structural changes in the lung produced by short-term, concomitant exposure to ozone and sulfuric acid, groups of 10 rats were exposed 4 hr/day for 2 days to filtered air, 0.6 ppm ozone, 0.5 mg/m3 fine (aerosol mass median diameter (MMD) = 0.3 microm) or ultrafine (MMD = 0.06 microm) sulfuric acid, or a mixture of ozone and 0.5 mg/m3 fine or ultrafine sulfuric acid. The volume percentage of total parenchyma containing markedly to severely injured alveolar septae was measured morphometrically. There were no differences between the ultrafine or fine acid exposure groups and the sham group for any of the morphologic endpoints. Volume percentage of markedly to severely injured tissue was increased in the ultrafine, but not fine, mixture animals when compared with the ozone-only group. In addition, a synergistic interaction between ozone and ultrafine, but not fine, sulfuric acid was found for this endpoint. The bromodeoxyuridine cell labeling index in the periacinar region was greater in the rats exposed to the fine sulfuric acid and ozone mixture than that in rats exposed to ozone alone, and a synergistic interaction between ozone and fine sulfuric acid was found for this end point. None of the exposures produced any changes in ventilatory parameters. Thus, acid aerosol droplet size was found to influence the effect of sulfuric acid in modifying ozone-induced structural changes in the rat lung.

Administration, Inhalation↗

PubMed1989

Structural change in academic health centers.

In response to opportunities and threats in their environments, academic health centers (AHCs) are making important changes in their structure. Several AHCs have legally separated their university hospital from the university. In contrast, other AHCs are linking the university hospital more closely to the medical school by concentrating authority for key decisions in the office of an AHC executive. This article draws from a national study of AHCs and examines the advantages and disadvantages of such changes in AHC structure. An important reason for these changes is maximizing revenues from patient care; an important consequence is the increased salience of patient care among the multiple purposes of AHCs.

Academic Medical Centers↗