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PubMed2006

The pH-dependent conformational states of kyotorphin: a constant-pH molecular dynamics study.

An extensive conformational study of the analgesic dipeptide kyotorphin (L-Tyr-L-Arg) at different pH values was performed using a constant-pH molecular dynamics method. This dipeptide showed a remarkable pH-dependent conformational variety. The protonation of the N-terminal amine was identified as a key element in the transition between the more extended and the more packed conformational states, as monitored by the dihedral angle defined by the atoms 1Cbeta-1Calpha-2Calpha-2Cbeta. The principal-component analysis of kyotorphin identified two major conformational populations (the extended trans and the packed cis) together with conformations that occur exclusively at extreme pH values. Other, less stable conformations were also identified, which help us to understand the transitions between the predominant populations. The fitting of kyotorphin's conformational space to the structure of morphine resulted in a set of conformers that were able to fulfill most of the constraints for the mu-receptor. These results suggest that there may be strong similarities between the kyotorphin receptor and the structural family of opioid receptors.

Computer Simulation↗
PubMed2005

Association of importance of the doctoral degree with students' perceptions and anticipated activities reflecting professionalism.

BACKGROUND AND PURPOSE: The American Physical Therapy Association (APTA) has identified the Doctor of Physical Therapy (DPT) degree as 1 of 6 elements necessary to transition the physical therapy profession to a fully professionalized discipline. However, there have been no data to determine whether physical therapist students who place importance on the DPT degree perceive physical therapy to be more professionalized or anticipate participation in activities reflecting professionalism more than those who do not place importance on the DPT degree. SUBJECTS: The subjects were 919 professional physical therapist students. METHODS: Faculty members at 34 physical therapist education programs distributed questionnaires to 1,172 professional physical therapist students and returned 919 questionnaires, for a response rate of 78.4%. The data were statistically analyzed using chi-square analysis and logistic regression. RESULTS: There were few differences between students who place importance on the DPT degree (DPT-I students) and those who do not place importance on the DPT degree (DPT-NI students) regarding how professionalized they perceive physical therapy to be relative to other health care professions or regarding their anticipated participation in activities reflecting professionalism. The one potential distinction found when controlling for other variables was that DPT-I students were more likely than DPT-NI students to anticipate becoming faculty members. DISCUSSION AND CONCLUSION: When beginning their professional education, there are few differences between DPT-I and DPT-NI students' perceptions of the professionalization of physical therapy or anticipation of activities reflecting professionalism.

Attitude of Health Personnel↗
PubMed1989

Reactive glioma in intracranial sarcoma ('sarcoglioma'). Histology, electron microscopy and immunohistochemistry of two additional cases.

The clinicopathologic features of 2 cases of sarcoglioma are described. This rare type of mixed brain tumor is composed of a central core of sarcoma with peripheral distribution of gliomatous elements with gradual transition from reactive to neoplastic astrocytes. The immunohistochemical features showed a strict positivity to glial fibrillary acidic protein only in glial cells, a positivity to vimentin prevalently in sarcomatous cells, whereas the factor VIII-related antigen was negative in astrocytes as well as in sarcomatous cells. The different origin of two neoplastic components is demonstrated well by an ultrastructural study. The morphological observations together with an adequate clinical setting contribute to separate this specific entity from other mixed brain tumors.

Antigens↗
PubMed1985

Models to predict operational loads of flight schedules.

Several concepts have been presented in the literature which have the potential to predict the operational load on aircrews during long-distance flights. They are briefly described and applied to a flight duty pattern actually scheduled for an airline route. For each model relative and absolute difficulty grades for the different segments of the pattern are evaluated and compared. Relative ranking results in an excellent agreement between the various models. Absolute classification into "normal," "heavy," and "definitely severe" segments reveals less conformity. From our observations on this route, it is concluded that the index of Mohler's model reflects the most realistic load estimates. Finally, a new approach is introduced which considers duty period, night flying, number of transits, preceding layover time, and preceding time-zone transitions as those elements constituting a computable and essential part of the operational load.

Aerospace Medicine↗
PubMed1983

Vanadium: chemistry and the kidney.

Vanadium (V), a metallic element of the first transition series, is widely distributed in the environment. Although an essential trace element in higher animals, chronic exposure to V is of concern because of its increased concentration near industrial operations, its occurrence in the ash of combustion products of petroleum and coal, and its subsequent biomagnification in the environment. V is found in trace amounts in both terrestrial and aquatic animals and in solution can form inorganic orthovanadate oxyanions that, if absorbed, are eliminated primarily by the kidneys. Because V is often found concentrated in renal tissue to the largest extent in the body, the kidneys may represent a major site of action. Moreover, V in the vanadate configuration increases the urinary excretion of solutes and water in the rat, and inhibits renal organic ion accumulation and renal Na+, K+-ATPase in vitro and in vivo. Furthermore, as a nutritionally required element, V may play a regulatory role in salt and water excretion by modification of the Na+ pump in the kidney.

Animals↗
PubMed1983

[Microcinematographic study of in vitro fusion between blood monocytes and differentiated osteoclasts].

The cell cycle of osteoclasts is hard to define, because regularly new nuclei enter in, and old nuclei are extruded from these polynucleated elements. The "transit-time" of a single nucleus averages 9-11 days in dogs and the factors conditioning this renewal are unknown. With the aim of elucidating in vitro the conditions necessary for the entrance of new nuclei in the polycarions, cultures of purified osteoclasts from medullary bone of laying hens and monocytes from circulating blood of the same animals have been performed after a previous period of 5 days of separate cultures each one of these two cell types. Part of the monocytes added to the osteoclast cultures, after a variable period of time entered in the polycarions by an active process of membrane fusion. Some phases of the process have been visualized at phase contrast and confirmed by time-lapse microcinematography and scanning electron microscopy.

Animals↗
PubMed1993

Identity of Saccharomyces cerevisiae tRNA(Trp) is not changed by an anticodon mutation that creates an amber suppressor.

A C35-->T mutation in an Escherichia coli tRNA(Trp) gene creates an amber suppressor which efficiently inserts glutamine in response to UAG codons in vivo (Soll, L., and Berg, P. (1969) Nature 223, 1340-1342). We have introduced the same change in a yeast tRNA(Trp) gene and demonstrated that the tRNA acts as an efficient amber suppressor in vivo. Amino acid sequence analyses were performed on chitinase produced by cells carrying the corresponding gene with a UAG codon at position 8 of the mature protein plus the mutant tRNA(Trp) gene. In contrast to comparable experiments with E. coli, tryptophan is inserted at a frequency > or = 80% by the yeast suppressor tRNA(Trp). Furthermore, in vitro charging experiments with the mutant tRNA(Trp) reveal no detectable increase in glutamine acceptor activity results from the C35-->T transition. The identity elements in E. coli tRNA(Gln) are well characterized (Jahn, M., Rogers, J., and Soll, D. (1991) Nature 352, 258-260). Sequence comparisons of the tRNA(Trp) and tRNA(Gln) molecules from E. coli reveal that the amber suppressor tRNA(Trp) has four of five identity elements required for glutaminyl-tRNA synthetase recognition. A similar comparison in the yeast system shows only two of the five potential identity elements are present. We conclude that, in spite of substantial structural similarities between yeast and E. coli aminoacyl-tRNA synthetases, fundamental differences can exist with regard to tRNA recognition.

Amino Acyl-tRNA Synthetases↗
PubMed1998

Mucoepidermoid carcinoma of the thyroid gland arising from a papillary epithelial neoplasm.

We report a case of mucoepidermoid carcinoma of the thyroid gland. The simultaneous association of papillary and mucoepidermoid carcinoma in a Hashimoto's thyroiditis makes the present observation unusual. Surgery was limited due to local extension of the neoplasm. The patient consequently underwent external radiotherapy followed by radiometabolic therapy. The patient survived 11 months after diagnosis. As far as the histogenesis of the neoplasm is concerned, we believe that mucoepidermoid areas correspond to squamous and mucinous metaplasia of a preexisting papillary carcinoma. Transition areas between elements morphologically characteristic of both neoplasms were observed. Histochemical and immunohistochemical studies confirmed the diagnosis of a carcinoma with multiple aspects showing a focal positive reaction for thyroglobulin or keratin antisera. Therefore, this demonstrates different functional activities of the neoplastic cells. There is still debate about adjuvant therapies, the results of which appear for the moment very poor.

Aged↗
PubMed1990

Precopulatory behaviour in male rats: ethological analysis and functional considerations.

Ethologically derived procedure was used to determine the appearance of precopulatory behavioural elements in adult male rats in the course of interaction with a behaviourally strictly defined female partner, the so-called Presenting female. The data obtained were tabulated in sequence tables of elements. Two versions were used with the aim to analyze an expected value for each cell and comparing this with the observed value. Flow diagrams were constructed to depict the appearance of the individual precopulatory elements as well as transitions among them. The results can be summarized as follows. The appearance of precopulatory elements in males interacted with Presenting female proceeds in a certain sequence. After the partners are close together, the typical sequence of short body-sniffing, anogenital exploration and touching the flank was found. The other elements - climbing over, circling around, manipulation, standing on - lack a similar regularity; the relations among them are rather complicated. If the male is not able to pass from the precopulatory to the copulatory phase, he reverts very often to the exhibition of the two out of three formerly exhibited elements, i.e. anogenital exploration and touching the flank. However, there are considerable interindividual as well as intraindividual differences in total frequencies of precopulatory elements. The results are discussed from a point of view of the optimum goal-directness of sexual interaction and compared with those achieved in the previous studies in which different stimulus females were used. Further, the function of the individual precopulatory elements of male rats in sexual interaction is reviewed. Finally, the precopulatory interaction is considered to be a communicative process by means of which the sex partners are approaching the transition into the copulatory phase.

Animals↗
PubMed1990

Chelation ion chromatography as a method for trace elemental analysis in complex environmental and biological samples.

The development and evaluation of a new method for the determination of trace transition and rare-earth elements based on the combination of chelation and ion chromatography are described. The new method, chelation ion chromatography (Chelation IC), uses a chelating column to concentrate and separate transition and rare-earth elements from the common alkali and alkaline-earth metals, as well as other matrix components, prior to analysis by ion chromatography. The sample fraction from the chelating column contains only the concentrated analyte ions, thus eliminating interfering matrix components from complex matrices such as seawater and digested biological, botanical, and geological materials. This combination of chelation and ion chromatography provides a technique that makes possible the determination of trace elements in complex matrices that have proven to be difficult or impossible to analyze by ion chromatography or conventional atomic spectroscopy techniques.

Animals↗
PubMed2006

The challenge of the so-called electron configurations of the transition metals.

Quite different meanings are attached by chemists to the words element, atom, orbital, order of orbitals or configurations. This causes conceptual inconsistencies, in particular with respect to the transition-metal elements and their atoms or ions. The different meanings will here be distinguished carefully. They are analyzed on the basis of empirical atomic spectral data and quasi-relativistic density functional calculations. The latter are quite reliable for different average configuration energies of transition-metal atoms. The so-called "configurations of the chemical elements", traditionally displayed in periodic tables, are the dominant configurations of the lowest spin-orbit levels of the free atoms. They are chemically rather irrelevant. In many-electron systems the ns and np AOs are significantly below the more hydrogen-like nd ones. Even (n+1)s is below nd for all light neutral atoms from C onwards, but only up to the first elements of the respective long rows! The most common orbital order in transition-metal atoms is 3p << 3d < 4s etc. The chemically relevant configuration in group g is always d(g) instead of d(g-2) s(2). Conceptually clear reasoning eliminates apparent textbook inconsistencies between simple quantum-chemical models and the empirical facts. The empirically and theoretically well-founded Rydberg (n-deltal) rule is to be preferred instead of the historical Madelung (n+l) rule with its large number of exceptions.

Journal Article↗
PubMed2002

Diet, health and the nutrition transition: some impacts of economic and socio-economic factors on food consumption patterns in the Kingdom of Tonga.

An essential element of the "health transition" is the emergence of disease patterns associated with changes in dietary regimes. The consumption of nutritionally poor (imported) foods in the Pacific is associated with increasing rates of diet related non-communicable diseases (NCDs). An oft-made assumption is that changes in consumption patterns are related to food preference (specifically preferences for high fat and/or dense carbohydrate foods). Recent work in the Kingdom of Tonga suggests that the "common-sense" association between food preference and food consumption is incorrect. The results of a large survey (n=430) indicate availability is the key factor in consumption, and that food preference, knowledge of the nutritional values of foods, and frequency of consumption are not correlated. Further analysis shows there are significant differences in consumption patterns between persons of higher and lower socio-economic status; perception of availability and frequency of consumption are a function of economic and social position--specifically access to cash. These results underline the salience of economic factors; the rise in NCDs is correlated with the increasing importance of the cash economy (not cultural values or ignorance of nutritional issues). In the absence of economic solutions, current consumption patterns will continue.

Adolescent↗
PubMed1985

Interactions of some naturally occurring cations with phenylalanine and initiator tRNA from yeast as reflected by their thermal stability.

The thermal unfolding of phenylalanine and initiator tRNA from yeast was investigated over a broad range of solution conditions by differential ultraviolet absorption at 260 nm. Under most conditions, the initiator tRNA exhibits two clearly separated transitions in its differential melting curve which were assigned to unfolding of tertiary and secondary structure elements, respectively. The tertiary transition of this tRNA and the overall transition observed for tRNAPhe do not show a maximum in a curve of Tm values plotted as a function of [Na+]. Such a maximum is usually observed for other nucleic acids at about 1 M Na+. In the presence of 5 mM of the divalent cation Mg2+ (or Ca2+), an overall destabilization of the tRNAs is observed when increasing the sodium concentration. The largest fall in Tm (approximately 15 degrees C) is observed for the tertiary transition of the initiator tRNA. Among various cations tested the following efficiency in the overall stabilization of tRNAPhe is observed: spermine greater than spermidine greater than putrescine greater than Na+ (approximately NH4+). Mg2+ is most efficient at concentrations above 5 mM, but below this concentration spermine and spermidine appear to be more efficient. The same hierarchy in stabilizing power of the polyamines and Na+ is observed for both transitions of the initiator tRNA. However, when compared with Mg2+, the polyamines are far less capable of stabilizing the tertiary structure. In contrast, spermine and spermidine are slightly better than Mg2+ in stabilizing the secondary structure. At increasing concentrations of the polyvalent cations (at fixed [Na+] ) the Tm values of the tRNAs attain a constant value.

Calcium↗
PubMed2006

Electronic structures and chemical bonding in transition metal monosilicides MSi (M = 3d, 4d, 5d elements).

Bond distances, vibrational frequencies, electron affinities, ionization potentials, dissociation energies, and dipole moments of the title molecules in neutral, positively, and negatively charged ions were studied using the density functional method. Ground state was assigned for each species. The bonding patterns were analyzed and compared with both the available data and across the series. It was found that besides an ionic component, covalent bonds are formed between the metal s,d orbitals and the silicon 3p orbital. The covalent character increases from ScSi (YSi) to NiSi (PdSi) for 3d (4d) metal monosilicides, then decreases. For 5d metal monosilicides, the covalent character increases from LaSi to OsSi, then decreases. For the dissociation of cations, the dissociation channel depends on the magnitude of the ionization potential between metal and silicon. If the ionization potential of the metal is smaller than that of silicon, channel MSi+ --> M+ + Si is favored. Otherwise, MSi+ --> M + Si+ will be favored. A similar behavior was observed for anions, in which the dissociation channel depends on the magnitude of electron affinity.

Journal Article↗
PubMed2001

Pseudosymmetry and phase transition in dimethyl 2,3-bis(tricyclo.

The crystal structure of the title compound, C(26)H(34)O(4), shows a reversible phase transition at about 178 K. The structure of the high-temperature phase contains two independent molecules related by pseudosymmetry elements. Cooling through the phase-transition temperature results in a doubling of the c axis. The low-temperature structure contains four independent molecules related by pseudosymmetry elements. The phase transition results in a rearrangement of some weak intermolecular C-H.O interactions. The number of very weak C-H.O interactions, with H.O distances between 2.8 and 2.9 A, is increased in the low-temperature structure.

Journal Article↗
PubMed1998

Agonist regulation of human beta2-adrenergic receptor mRNA stability occurs via a specific AU-rich element.

Prolonged agonist stimulation of beta2-adrenergic receptors results in receptor down-regulation, which is closely associated with a reduction of the corresponding mRNA, an effect mediated in part by changes in mRNA stability. Transfection experiments with human beta2-adrenergic receptor cDNAs bearing or lacking the untranslated regions suggested that the essential agonist sensitivity of the mRNA resides within the 3'-untranslated region. The importance of this region was further confirmed in gel shift experiments; cytosolic preparations from agonist-stimulated DDT1-MF2 smooth muscle cells caused a shift of beta2-adrenergic receptor mRNAs containing the 3'-untranslated region. Progressive 3'-terminal truncations of the receptor cDNA led to the identification of an AU-rich element at positions 329-337 of the 3'-untranslated region as the responsible cis-acting element. Substitution of this motif by cytosine residues almost completely abolished mRNA down-regulation and inhibited the formation of the RNA-protein complex. Even though the beta2-adrenergic receptor AU-rich element showed two U --> A transitions compared with the recently proposed AU-rich element consensus sequence, it revealed an almost identical destabilizing potency. Fusion of the beta2-adrenergic receptor 3'-untranslated region to the beta-globin coding sequence dramatically reduced the half-life of the chimeric transcript in an agonist- and cAMP-dependent manner. This suggests that the agonist-induced beta2-adrenergic receptor mRNA destabilization is regulated by cAMP-dependent RNA-binding protein(s) via a specific AU-rich element.

Adrenergic beta-2 Receptor Agonists↗
PubMed1984

Transition metals in human cancer II.

Many of the trace metals are associated with enzymes involved in vital physiological roles. It would therefore seem reasonable to expect alterations in the levels of certain elements to be associated with cancer. Secondly, their levels would indicate whether or not they have a direct influence on the proton spin-lattice relaxation time (T1), as determined by pulsed nuclear magnetic resonance spectrometry (NMR). The results obtained on leukaemic bone marrow and oesophageal cancer were reported earlier. In the present work is reported the data obtained for the levels of the transition elements Fe, Zn, Mn and Cu in human cancers of other regions of the body. The role of trace metals has been discussed from the point of view both of their value as markers of malignancy, and of the elevation of proton spin-lattice relaxation times.

Copper↗