Development of cytochrome-c oxidase activity in rat heart

3′-azido-3′-deoxythymidine (AZT) is the first effective drug used clinically for the treatment of human immunodeficiency virus (HIV) infection. The drug interactions with DNA and protein are associated with its mechanism of action in vivo. This study was designed to examine the interaction of AZT with the Na,K-dependent adenosine triphosphatase (Na,K-ATPase) in H₂O and D₂O solutions at physiological pH using drug concentration of 0.1 μM to 1 mM and final protein concentration of 0.5 to 1 mg/mL. Ultraviolet absorption and Fourier transform infrared difference spectroscopy with its self-deconvolution second-derivative resolution enhancement, and curve-fitting procedures were used to characterize the drug-binding mode, the drug-binding constant, and the effects of drug interaction on the protein secondary structure Spectroscopic evidence showed that at low drug concentration (0.1 μM), AZT binds (H-bonding) mainly to the polypeptide C=O and C−N groups with two binding constants of K₁=5.3×10⁵ M ⁻¹ and K₂=9.8×10³ M ⁻¹. As drug content increased, AZT-lipid complex prevailed. At a high drug concentration (1 mM), drug binding resulted in minor protein secondary structural changes from that of the α-helix 19.8%; β-pleated 25.6%; turn 9.1%; β-antiparallel 7.5% and random 38%, in the free Na,K-ATPase to that of the α-helix 19%; β-pleated 21.1%; turn 10.1%; β-antiparallel 8.8% and random 41%, in the AZT-ATPase complexes.     

Docosahexaenoic acid and eicosapentaenoic acid are converted by 3T3-L1 adipocytes to N-acyl ethanolamines with anti-inflammatory properties

n-3 PUFAs have beneficial health effects which are believed to be partly related to their anti-inflammatory properties, however the exact mechanisms behind this are unknown. One possible explanation could be via their conversion to N-acyl ethanolamines (NAEs), which are known to possess anti-inflammatory properties. Using fatty acid precursors we showed that 3T3-L1 adipocytes are indeed able to convert docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) to their NAE derivatives docosahexaenoyl ethanolamine (DHEA) and eicosapentaenoyl ethanolamine (EPEA), respectively. This synthesis took place on top of an apparent background formation of these NAEs in standard culture medium. In addition we were able to demonstrate the presence of DHEA, but not of EPEA, in human plasma. DHEA and EPEA were found to decrease LPS induced adipocyte IL-6 and MCP-1 levels. Results of combined incubations with PPAR-γ and CB2 antagonists suggest a role of these receptors in mediating the reduction of IL-6 by DHEA. Our results are in line with the hypothesis that in addition to other pathways, formation of N-acyl ethanolamines may contribute to the biological activity of n-3 PUFAs. Different targets, including the endocannabinoid system, may be involved in the immune-modulating activity of these “fish-oil-derived NAEs.”     

Normal‐mode‐based modeling of allosteric couplings that underlie cyclic conformational transition in F1 ATPase

F₁ ATPase, a rotary motor comprised of a central stalk ( γ subunit) enclosed by three α and β subunits alternately arranged in a hexamer, features highly cooperative binding and hydrolysis of ATP. Despite steady progress in biophysical, biochemical, and computational studies of this fascinating motor, the structural basis for cooperative ATPase involving its three catalytic sites remains not fully understood. To illuminate this key mechanistic puzzle, we have employed a coarse‐grained elastic network model to probe the allosteric couplings underlying the cyclic conformational transition in F₁ ATPase at a residue level of detail. We will elucidate how ATP binding and product (ADP and phosphate) release at two catalytic sites are coupled with the rotation of γ subunit via various domain motions in α ₃ β ₃ hexamer (including intrasubunit hinge‐bending motions in β subunits and intersubunit rigid‐body rotations between adjacent α and β subunits). To this end, we have used a normal‐mode‐based correlation analysis to quantify the allosteric couplings of these domain motions to local motions at catalytic sites and the rotation of γ subunit. We have then identified key amino acid residues involved in the above couplings, some of which have been validated against past studies of mutated and γ ‐truncated F₁ ATPase. Our finding strongly supports a binding change mechanism where ATP binding to the empty catalytic site triggers a series of intra‐ and intersubunit domain motions leading to ATP hydrolysis and product release at the other two closed catalytic sites. Proteins 2009. © 2009 Wiley‐Liss, Inc.     

Elementary mode analysis: a useful metabolic pathway analysis tool for characterizing cellular metabolism

Elementary mode analysis is a useful metabolic pathway analysis tool to identify the structure of a metabolic network that links the cellular phenotype to the corresponding genotype. The analysis can decompose the intricate metabolic network comprised of highly interconnected reactions into uniquely organized pathways. These pathways consisting of a minimal set of enzymes that can support steady state operation of cellular metabolism represent independent cellular physiological states. Such pathway definition provides a rigorous basis to systematically characterize cellular phenotypes, metabolic network regulation, robustness, and fragility that facilitate understanding of cell physiology and implementation of metabolic engineering strategies. This mini-review aims to overview the development and application of elementary mode analysis as a metabolic pathway analysis tool in studying cell physiology and as a basis of metabolic engineering.     

Differential Effects of an Intense Wildfire on Survival of Sympatric Snakes

Abstract: We analyzed 16 years of mark-recapture data to investigate whether a wildfire influenced survival of an arboreal ambush-forager (broad-headed snake [Hoplocephalus bungaroides]) and a terrestrial active forager (small-eyed snake Cryptophis nigrescens). We predicted that wildfire would cause direct mortality and reduce subsequent survival of both snake species. Contrary to this prediction, wildfire did not affect abundance of broad-headed snakes, but abundance of small-eyed snakes decreased by 48% after the wildfire. Estimated annual survival of small-eyed snakes was 37% lower after fire (s=0.47, SE=0.07) than before fire (s=0.74, SE=0.05). Prescribed burning may be a suitable tool for creating open habitat mosaics for the endangered broad-headed snake.     

Age-Sex Analysis of Activity Budget,Diet, and Positional Behavior in <Emphasis Type="Italic">Alouatta caraya</Emphasis> in an Orchard Forest

Howlers (Alouatta spp.) spend more than half of the daytime resting and their diet consists predominantly of leaves. Associated with a general strategy of energy conservation, their positional behavior is characterized by quadrupedalism as the major locomotor mode, and sitting as the most common resting and feeding posture. However, researchers have sparse information on the degree to which age-sex classes fit the generic trends and the influence of habitat structure on them. We compare the activity budget, dietary composition, and positional behavior by age-sex or age classes in a group of black-and-gold howlers (Alouatta caraya) in a small orchard forest. We collected 26,474 behavioral records via instantaneous scan sampling over 1 yr. The main activity was resting (56%) and the diet comprised mainly leaves (82%); sitting was the most adopted feeding (61%) and resting (52%) posture, and walking was the most prevalent locomotor mode (38%). There are age-sex differences for all major behaviors. Whereas resting tended to increase with body size, moving decreased. We observed no difference in the consumption of major plant parts. There were ontogenetic differences in most positional behaviors. Sitting increased from infants to adults during feeding, whereas the opposite occurred for bridging and hanging. During resting, infants curled more and lay less than the other classes did, whereas adults engaged in more sitting. Adults and subadults walked more than individuals of other ages did; infants climbed and bridged more than others did; and, there were opposing trends in leaping and descending. Habitat structure is a partial explanation of the locomotor behavior of black-and-gold howlers.     

Medical students as medical educators: opportunities for skill development in the absence of formal training programs

All physicians, at some point in their career, are responsible for the education of their peers and junior colleagues. Although medical students are expected to develop clinical and research skills in preparation for residency, it is becoming clear that a student should also be expected to develop abilities as a teacher. A handful of institutions have student-as-teacher programs to train medical students in education, but most students graduate from medical school without formal training in this area. When such a program does not exist, medical students can gain experience in education through participation in peer teaching, course design, educational committees, and medical education scholarship. In doing so, they attain important skills in the development, implementation, and evaluation of educational programs. These skills will serve them in their capacity as medical educators as they advance in their careers and gain increasing teaching responsibility as residents, fellows, and attending physicians.     

国外继续教育模式对我国继续医学教育的启示

分析国外先进继续教育模式,总结我国继续教育存在的问题和困难,主要包括：法律法规不健全、形式相对单一、培养模式普教化、市场运行机制尚未健全、实践教学相对薄弱、师资队伍建设滞后。借鉴国外经验提出几点启示：健全医学继续教育法律法规及监控体系、加强校企合作、完善市场机制、加强实践教学、完善评估体系。     

Relation between sequence and structure of HIV-1 protease inhibitor complexes: a model system for the analysis of protein flexibility.

The flexibility of different regions of HIV-1 protease was examined by using a database consisting of 73 X-ray structures that differ in terms of sequence, ligands or both. The root-mean-square differences of the backbone for the set of structures were shown to have the same variation with residue number as those obtained from molecular dynamics simulations, normal mode analyses and X-ray B-factors. This supports the idea that observed structural changes provide a measure of the inherent flexibility of the protein, although specific interactions between the protease and the ligand play a secondary role. The results suggest that the potential energy surface of the HIV-1 protease is characterized by many local minima with small energetic differences, some of which are sampled by the different X-ray structures of the HIV-1 protease complexes. Interdomain correlated motions were calculated from the structural fluctuations and the results were also in agreement with molecular dynamics simulations and normal mode analyses. Implications of the results for the drug-resistance engendered by mutations are discussed briefly.