Divalent Cation Stimulation of Substrate Oxidation by Corn Mitochondria

The oxidation of reduced nicotinamide adenine dinucleotide, malate-pyruvate, and succinate by corn mitochondria in buffered 0.2 m KCl was determined as a function of divalent cations. Ni 2+ , Mg 2+ , Co 2+ , Ca 2+ , Mn 2+ , Sr 2+ , and Ba 2+ stimulated reduced nicotinamide adenine dinucleotide oxidation in the absence of inorganic phosphate, with Ca 2+ and Sr 2+ having the greatest effect. Malate-pyruvate and succinate oxidation was stimulated by Ca 2+ , Ba 2+ , and Sr 2+ , but only in the presence of inorganic phosphate. Ca 2+ , Sr 2+ , and Ba 2+ produced a simulated state 4 to state 3 transition with all three substrates, but only with malate-pyruvate and succinate was there a return to state 4. The order of divalent cation effectiveness suggests that the rate of water substitution from the cation inner coordination hydration sphere may be a rate-limiting step in certain mitochondrial reactions involving electron transport and phosphorylation.