Systematics within Gyps vultures: a clade at risk

Background  

Populations of the Oriental White-backed Vulture (Gyps bengalensis) have declined by over 95% within the past decade. This decline is largely due to incidental consumption of the non-steroidal anti-inflammatory veterinary pharmaceutical diclofenac, commonly used to treat domestic livestock. The conservation status of other Gyps vultures in southern Asia is also of immediate concern, given the lack of knowledge regarding status of their populations and the continuing existence of taxonomic uncertainties. In this study, we assess phylogenetic relationships for all recognized species and the majority of subspecies within the genus Gyps. The continuing veterinary use of diclofenac is an unknown but potential risk to related species with similar feeding habits to Gyps bengalensis. Therefore, an accurate assessment of the phylogenetic relationships among Gyps vultures should aid in their conservation by clarifying taxonomic uncertainties, and enabling inference of their respective relatedness to susceptible G. bengalensis.     

Pathway of acetate assimilation in autotrophic and heterotrophic methanococci.

The autotroph Methanococcus maripaludis contained high levels of acetate-coenzyme A ligase, pyruvate synthase, pyruvate, water dikinase, pyruvate carboxylase, and the enzymes of the incomplete reductive tricarboxylic acid cycle. Phosphoenolpyruvate carboxykinase, citrate synthase, and isocitrate dehydrogenase were not detected. In contrast, the heterotroph Methanococcus sp. strain A3 contained acetate kinase, and acetate coenzyme A ligase was virtually absent.     

Temperature-induced protein conformational changes in barley root plasma membrane-enriched microsomes: I. Effect of temperature on membrane protein and lipid mobility

A protein spin label and lipid spin probes were used to study the temperature-dependent motion of protein and lipid, respectively, in barley (Hordeum vulgare L. cv Conquest) root plasma membrane-enriched microsomes. Using membranes from seedlings grown at 20°C, the temperature-dependence of the relative motion of membrane surface spin probes and a spin label covalently attached to membrane proteins suggested abrupt changes in the lipid and protein mobilities at about 12°C. Spin probe spin-spin exchange broadening and fluorescent probe eximer formation indicated apparent temperature-induced alterations in probe lateral diffusion within the membrane at about 12 to 14°C. The results suggest the presence of temperature-induced quasicrystalline lipid clusters which may influence the activity of membrane-bound enzymes.     

Symmetry and asymmetry in mandelate racemase catalysis

Kinetic properties of mandelate racemase catalysis (Vmax, Km, deuterium isotope effects, and pH profiles) were all measured in both directions by the circular dichroic assay of Sharp et al. [Sharp, T. R., Hegeman, G. D., & Kenyon, G. L. (1979) Anal. Biochem. 94, 329]. These results, along with those of studying interactions of mandelate racemase with resolved, enantiomeric competitive inhibitors [(R)- and (S)-alpha-phenylglycerates], indicate a high degree of symmetry in both binding and catalysis. Racemization of either enantiomer of mandelate in D2O did not show an overshoot region of molecular ellipticity in circular dichroic measurements upon approach to equilibrium. Both the absence of such an overshoot region and the high degree of kinetic symmetry are consistent with a one-base acceptor mechanism for mandelate racemase. On the other hand, results of irreversible inhibition with partially resolved, enantiomeric affinity labels [(R)- and (S)-alpha-phenylglycidates] reveal a "functional asymmetry" at the active site. Mechanistic proposals, consistent with these results, are presented.     

Activation of the methylreductase system from Methanobacterium bryantii by ATP.

The methylreductase of Methanobacterium bryantii required ATP for activity. There was sufficient ATP synthesis in extracts to account for the observed activity. Hexokinase inhibited the methylreductase by competing for endogenously synthesized ATP. The uncoupler, carbonyl cyanide p-trifluoromethyoxyphenyl hydrazone, inhibited only at concentrations greater than 0.5 mM, and detergents and non-halogenated membrane-permeable-ions did not inhibit. Thus, membrane proton gradients are not important in activation. In addition, maximal activation was obtained with less than 0.25 mM ATP, was inhibited by beta, gamma-imido ATP, and was strongly temperature dependent. The activated state was very unstable, having a half-life of 5 to 15 min. After gel filtration at 5 degrees C, the methylreductase retained partial activity for a short time in the absence of ATP. These observations indicate that activation involves the modification of a protein or protein-bound cofactor of the methylreductase system.     

Patterns of divergence during evolution of alpha 1-proteinase inhibitors in mammals

alpha 1-Proteinase inhibitor (alpha 1-PI), a member of the serine proteinase inhibitor superfamily, has a primary role in controlling neutrophil elastase activity within the mammalian circulation. Several studies have indicated that the reactive center region of alpha 1-PI, the amino acid sequence of which is critical to recognition of and binding to target proteinases, is highly divergent within and among species. This appears to be a consequence of accelerated rates of evolution that may have been driven by positive Darwinian selection. In order to examine this and other features of alpha 1-PI evolution in more detail, we have isolated and sequenced cDNAs representing alpha 1- PI mRNAs of the mouse species Mus saxicola and Mus minutoides and have compared these with a number of other mammalian alpha 1-PI mRNAs. Relative to other mammalian mRNAs, the extent of nonsynonymous substitution is generally high throughout the alpha 1-PI mRNA molecule, indicating greater overall rates of amino acid substitution. Within and among mouse species, the 5'-half of the mRNA, but not the 3'-half, has been homogenized by concerted evolution. Finally, the reactive center is under diversifying or positive Darwinian selection in murid rodents (rats, mice) and guinea pigs yet is under purifying selection in primates and artiodactyls. The significance of these findings to alpha 1-PI function and the possible selective forces driving evolution of serpins in general are discussed.