Mitochondrial Activity in Rainbow Trout Red Muscle: the Effect of Temperature on the Adp-dependence of Atp Synthesis

By coupling mitochondrial ATP production to an enzymatic NADPH-producing reaction, we monitored the rates of ATP production spectrophotometrically. ATP production was coupled to the oxidation of malate and pyruvate. Interference by adenylate kinase was eliminated by using P1,P5-di(adenosine-59)pentaphosphate and we found no interference by NADPH oxidase. We studied the kinetics of ATP synthesis by mitochondria from rainbow trout red muscle at three temperatures (8, 15 and 22 ̊C) and under two pH regimes (a constant pH of 7.4 and temperature-dependent pH). The mitochondria oxidized pyruvate and malate. The apparent Michaelis constant (Km,app) for ADP as well as the maximal velocity (Vmax) for ADP phosphorylation are markedly affected by temperature but not by pH. The Km,app for ADP decreases with increasing temperature while the Vmax increases. These data suggest that reduced temperatures decrease mitochondrial sensitivity to control by ADP availability.