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Biomedical subjects

R E DAVIES

Publications and source records attributed to R E DAVIES.

At least 19 recordsLinked to original sources
PubMed1964

ADENOSINE TRIPHOSPHATE: CHANGES IN MUSCLES DOING NEGATIVE WORK.

Frog sartorius muscles were isolated, treated with 1-fluoro-2, 4-dini-trobenzene at 0 degrees C, then stimulated tetanically at the length in situ and stretched with a Levin-Wyman ergometer during stimulation. The normal adenosine triphosphate breakdown during the tetanus was reduced by about half during the forced stretch. The tension was increased by about 70 percent, but resynthesis of adenosine triphosphate did not occur. Thus, on the basis of A. V. Hill's results, adenosine triphosphate is probably not the direct final energy source for muscular contraction, although it intimately participates in the process. The use of adenosine triphosphate during negative work was less than one-tenth that needed for positive work.

Adenosine Triphosphate↗
PubMed1962

Accumulation of sulfate by mitochondria of rat kidney cortex.

Twice washed mitochondria from rat kidney cortex can accumulate sulfate ions from low (10(-7)M) ambient concentrations to create virtual gradients of several hundred to one. This sulfate is subsequently released. The activation energy for the uptake is 12,000 calories per mole; for release it is about 30,000 calories per mole. Variations in the sulfate concentration of the medium show that there is a straight line Freundlich adsorption isotherm over a million-fold range of concentration of sulfate in the medium. There are 9 x 10(4) sites at 10(-5)M and 9 x 10(5) sites at 10(-3)M sulfate per average single mitochondrion. Preincubation at 30 degrees C rapidly destroys the ability to accumulate sulfate. Partial protection occurs if oxidative phosphorylation is proceeding during the preincubation. The concentration of the endogenous inorganic sulfate of twice washed mitochondria is 4.2 x 10(-4) moles per liter of mitochondrial pellet water; 99.85 per cent of this endogenous sulfate is inexchangeable with external sulfate in vitro. It is all exchangeable in vivo. The pH optimum for accumulation of radiosulfate from dilute external sulfate concentrations is 5.5. These observations show that there is a delicate and specific mechanism in mitochondria from kidney cortex which accumulates sulfate. The chemical nature of the accumulated sulfate is unknown.

Animals↗