Supplemental growth hormone alters body composition, muscle protein metabolism and serum lipids in fit adults: characterization of dose-dependent and response-recovery effects.

Using double-blind, placebo-controlled procedures, the effects of low and high therapeutic dosages of methionyl-human growth hormone (met-hGH) on body composition, muscle protein metabolism and serum lipids were studied in 7 fit adults without growth hormone (GH) deficiency. Dose-dependent changes in body composition were observed that in part appeared to be influenced by a response-recovery effect, as measured by responses factored according to the duration of washout between exposure to the low and high dosages of met-hGH (6 weeks vs. 12 weeks vs.

Fetal hyperinsulinemia and protein turnover in fetal rat tissues.

The effects of fetal hyperinsulinemia on protein turnover in various tissues of fetal rats were determined after transuteral injection of insulin to rat fetuses at day 19 of gestation. Tissue protein content was measured on the subsequent days of gestation (days 20-22), and protein synthesis was determined at day 20 of gestation in fetal tissues after intravenous injection of [3H]phenylalanine into the maternal circulation, followed by measurements of tissue free and protein-bound phenylalanine specific radioactivity in fetal diaphragm, brain, heart, and liver. Rates of protein degradation in these fetal tissues were calculated by subtracting protein accretion rates from rates of protein synthesis.

Protein turnover in tissues of the rat fetus following maternal starvation.

The effects of maternal starvation upon protein turnover in various tissues of the fetal rat were determined. Protein synthesis was determined in fetal tissues by the intravenous injection of "massive" amounts of 3H-phenylalanine into the maternal circulation, followed by measurements of tissue free and protein-bound phe specific radioactivity in fetal diaphragm, heart, liver, and brain. Rates of protein degradation in fetal tissues were assessed by subtracting protein accretion rates from protein synthesis.

The role of spermine in preventing misacylation by phenylalanyl-tRNA synthetase.

Physiological concentrations of polyamines contribute significantly to both the speed and precision of aminoacylation of tRNA. Unphysiologically high concentrations of magnesium ion are required to obtain high rates of synthesis of phenylalanyl-tRNAPheyeast catalyzed by yeast phenylalanine:tRNA ligase in vitro. Under such conditions, rates of misacylation (e.

Conformational changes during enzyme catalysis: role of water in the transition state.

The entropy of activation for the synthesis of Ile-tRNA is high and positive. The only likely source of a high delta S is the loss of structured water as the enzyme . substrate complex moves toward the transition state.

The mechanism of the aminoacylation of transfer ribonucleic acid. The kinetics and stoichiometry of the lysis of aminoacyl-tRNA.

It is often stated that the aminoacylation of transfer RNA proceeds in discrete steps: (formula: see article). If this is a complete description of the reaction, the reverse overall formation of ATP should not be more rapid than the formation of Enz . (AA approximately AMP).

The mechanism of the aminoacylation of transfer ribonucleic acid: enzyme-product dissociation is not rate limiting.

It has been proposed that the rate-limiting step in the synthesis of aminoacyl-tRNA is the rate at which the product dissociates from the enzyme. The experimental evidence supporting this hypothesis comes from work at low pH and low temperature (although the reaction has been argued to have the same mechanism under physiological conditions). We have reexamined the binding assay by which M.

The mechanism of aminoacylation of transfer ribonucleic acid. Reactivity of enzyme-bound isoleucyl adenylate.

Isoleucyl adenylate bound to isoleucine:tRNA ligase of Escherichia coli (EC 6.1.1.

Molecular order of participation of inhibitors (or activators) in biological systems.

From a Hill plot it is frequently possible to determine whether exactly one, two, or several inhibitor (or activator) molecules are involved in a critical rate-determining biological process.