Warm-up rates during arousal from torpor in heterothermic mammals: physiological correlates and a comparison with heterothermic insects

Summary This study examines the relationship between warm-up rate, body mass, metabolic rate, thermal conductance and normothermic body temperature in heterothermic mammals during arousal from torpor. Predictions based on the assumption that the energetic cost of arousal has been minimised are tested using data for 35 species. The observation that across-species warm-up rate correlates negatively with body mass is confirmed using a comparative technique which removes confounding effects due to the non-independence of species data due to shared common ancestry. Mean warm-up rate during arousal correlates negatively with basal metabolic rate and positively with the temperature difference through which the animal warms, having controlled for other factors. These results suggest that selection has operated to minimise the overall energetic, cost of warm-up. In contrast, peak warm-up rate during arousal correlates positively with peak metabolic rate during arousal, and negatively with thermal conductance, when body mass has been taken into account. These results suggest that peak warm-up rate is more sensitive to the fundamental processes of heat generation and loss. Although heterothermic marsupials have lower normothermic body temperatures and basal metabolic rates, marsupials and heterothermic eutherian mammals do not differ systematically in warm-up rate. Pre-flight warm-up rates in one group of endothermic insects, the bees, are significantly higher than predictions based on rates of arousal of a mammal of the same body mass.Abbreviations BMR basal metabolic rate - ICM independent comparisons method - MWR mean warm-up rate - PMR peak metabolic rate - PWR peak·warm-up rate - Tb_activity body temperature during activity - Tb_torpor body temperature during torpor - T _arousal increase in body temperature during arousal     

Mechanistic studies on thrombin catalysis

The kinetic mechanism of the cleavage of four p-nitroanilide (pNA) substrates by human alpha-thrombin has been investigated by using a number of steady-state kinetic techniques. Solvent isotope and viscosity effects were used to determine the stickiness of the substrates at the pH optimum of the reaction; a sticky substrate is defined as one that undergoes catalysis faster than it dissociates from the Michaelis complex. Whereas benzoyl-Arg-pNA could be classified as a nonsticky substrate, D-Phe-pipecolyl-Arg-pNA was very sticky. The other two substrates (tosyl-Gly-Pro-Arg-pNA and acetyl-D-Phe-pipecolyl-Arg-pNA) were slightly sticky. The pH profiles of kcat/Km were bell-shaped for all substrates. The pKa values determined from the pH dependence of kcat/Km for benzoyl-Arg-pNA were about 7.5 and 9.1. Similar pKa values were determined from the pH profiles of kcat/Km for tosyl-Gly-Pro-Arg-pNA and acetyl-D-Phe-pipecolyl-Arg-pNA and for the binding of the competitive inhibitor N alpha-dansyl-L-arginine-4-methylpiperidine amide. The groups responsible for the observed pKa values were proposed to be His57 and the alpha-amino group of Ile16. The temperature dependence of the pKa values was consistent with this assignment. The pKa values of 6.7 and 8.6 observed in the pH profile of kcat/Km for D-Phe-pipecolyl-Arg-pNA were displaced to lower values than those observed for the other substrates. The displacement of the acidic pKa value could be attributed to the stickiness of this substrate.(ABSTRACT TRUNCATED AT 250 WORDS)     

Specific interaction of vitronectin with the cell-secreted protease inhibitor glia-derived nexin and its thrombin complex.

Interaction of vitronectin with glia-derived nexin (GDN), thrombin, and the complex GDN-thrombin was demonstrated in direct binding assays that indicated the formation of binary and ternary complexes. The concentration of vitronectin necessary to obtain 50% saturation of the immobilized GDN-thrombin complex binding sites (EC50) was about 1 nM. Under similar experimental conditions, the EC50 of vitronectin for the immobilized antithrombin-III-thrombin complex was about fivefold higher. A tight complex was also formed between vitronectin and immobilized GDN (EC50 approximately 1.5 nM) but when vitronectin was immobilized, GDN displayed a reduced affinity for vitronectin (EC50 approximately 10 nM). These results suggest differences between the immobilized and free conformations of GDN and/or vitronectin. In contrast, vitronectin displayed negligible affinity for antithrombin III. Biotinylated GDN was used to characterize further the binding of GDN or the GDN-thrombin complex to vitronectin. The interaction of the biotinylated GDN-thrombin complex with immobilized vitronectin (EC50 approximately 2 nM) was completely blocked by nonbiotinylated complexes of thrombin with either GDN or antithrombin III, whereas free GDN, free thrombin and the GDN-trypsin complex were only weak competitors. Active-site-blocked urokinase and the complex GDN-urokinase also strongly competed for binding of the biotinylated GDN-thrombin complex to vitronectin. Binding of biotinylated GDN to immobilized vitronectin was specific, saturable and was competed with decreasing efficiency by the GDN-thrombin complex, free GDN and free antithrombin III. These interactions between the adhesive component vitronectin and the serine protease inhibitor GDN may relate to localized control of thrombin and/or urokinase action at certain extravascular sites. These results are discussed in terms of binding sites for vitronectin on GDN, thrombin, and the GDN-thrombin complex.     

Filicidal Ring-Y Chromosomes in D. MELANOGASTER

Ring-Y chromosomes are recovered infrequently from crosses of ring-Y-bearing males to females of certain strains (Oster 1964). Experiments described here have unveiled a diverse class of genes that exert a maternal effect on the behavior during cleavage of these "filicidal" ring chromosomes. Cytological observations of inviable embryos have revealed that the ring-Y chromosome causes gross disorganization of the cleavage nuclei. This inviability may be equivalent to the "dominant lethality" attributed to unstable ring-X chromosomes (Hinton 1955; Pasztor 1971). Mapping studies indicate that no single region of the normal Y is solely responsible for the unusual behavior of ring-Y chromosomes.