Vitellogenesis by the American cockroach: Haemolymph and follicle protein patterns during vitellogenin synthesis

Radioactive ¹⁴C-leucine is removed from the blood within 4 hr of injection during the first 2 days of the vitellogenic cycle. Injections during the 3rd to 6th day result in leucine retention and a rise in labelled protein.Label appears in the follicle by day 3 with most of the protein being incorporated during day 5. Comparison of haemolymph and follicle proteins suggests that fat body synthesis, subsequent haemolymph transport and follicle uptake all occur primarily on days 4 and 5 of the cycle.In vivo follicle incubations reveal ¹⁴C-leucine uptake during the last 4 days of the cycle. During days 4, 5, and 6, leucine is incorporated into protein by the follicle. Injections of ¹⁴C-haemolymph proteins into 6 day females result in the incorporation of label into the terminal oöcytes.     

A three‐dimensional potential of mean force to improve backbone and sidechain hydrogen bond geometry in Xplor‐NIH protein structure determination

We introduce a new hydrogen bonding potential of mean force generated from high‐quality crystal structures for use in Xplor‐NIH structure calculations. This term applies to hydrogen bonds involving both backbone and sidechain atoms. When used in structure refinement calculations of 10 example protein systems with experimental distance, dihedral and residual dipolar coupling restraints, we demonstrate that the new term has superior performance to the previously developed hydrogen bonding potential of mean force used in Xplor‐NIH.     

Dehydroepiandrosterone and Body Fat

Dehydroepiandrosterone sulfate (DHEA-S) is the most abundant circulating adrenal steroid in man, yet its physiologic role and that of its parent compound DHEA are unknown. Age-related decreases in DHEA in association with increases in obesity, insulin resistance, and atherosclerosis are well known. Recent investigations in lower mammals (which do not secrete DHEA) have suggested that DHEA (or its metabolites) may function as an antiobesity agent in these models of obesity independent of food intake. Proposed mechanisms for the decrease in fat mass and lower weight gain when DHEA is given orally include increases in futile cycling and peroxisomal β-oxidation and decreases in de novo lipogenesis. Alterations in the availability of reducing equivalents for lipid synthesis do not appear to explain this decrease. Changes in pancreatic insulin secretion or insulin sensitivity may also be responsible for some of these effects. Studies in humans have failed to demonstrate a beneficial effect of DHEA on body composition or energy expenditure at either pharmacologic or physiologic replacement doses for 1–3 months. Administration of DHEA to men or women has also not been shown to alter insulin sensitivity as measured by the minimal model or the euglycemic clamp technique. The effect of DHEA on peroxisomal β-oxidation and de novo lipogenesis is not known. We conclude that a significant role for DHEA in the pharmacologic treatment of human obesity is unlikely.     

CO binding to mitochondrial mixed valence state cytochrome oxidase at low temperatures

The kinetics and thermodynamics of the reaction of mixed valence state membrane-bound cytochrome oxidase with CO over the 178-203 K range has been studied by multichannel optical spectroscopy at three wavelength pairs (444-463 nm in the Soret region, and 590-630 and 608-630 nm in the alpha region) and analysed by non-linear optimization techniques. As in the case of the fully reduced membrane-bound cytochrome oxidase-CO reaction (Clore, G.M. and Chance, E.M. (1978) Biochem J. 175, 709-725), the normalized progress curves at the three wavelength pairs are significantly different indicating, on the basis of Beer's law, the presence of a minimum of three optically distinct species. The only model that satisfies the triple statistical requirement of a standard deviation within the standard error of the data, a random distribution of residuals and good determination of the optimized parameters, is a two species sequential mechanism: flash photolysis of the mixed valence state cytochrome oxidase-CO complex (species IIMC) yields unliganded mixed valence state cytochrome oxidase (species EM) and free CO which then recombine to form species IMC; species IMC is then converted into species IIMC. All the thermodynamic parameters describing the model are calculated and compared to those obtained for the fully reduced membrane-bound cytochrome oxidase-CO reaction (Clore and Chance (1978) Biochem. J. 175, 709-725). Although there are some qualitative similarities in the kinetics and thermodynamics of the reactions of mixed valence state (alpha 23+Cu+B.ALPHA 3+Cu2+A) and fully reduced (a3 2+Cu B + . a2+Cu A+) cytochrome oxidase with CO, there are large and significant quantitative differences in zero-point activation energies and frequency factors; over the temperature range studied, the mixed valence state cytochrome oxidase-CO reaction is found to proceed at a significantly slower rate than the fully reduced cytochrome oxidase-CO reaction. These differences indicate that changing the valence states of cytochrome a and CuA has a significant effect on the CO binding properties of cytochrome a 3 and possibly CuB.