FISHER
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Respiration of Rat Lung Mitochondria and the Influence of Ca2+ on Substrate Utilization? Aron B. Fisher,* Antonio Scarpa, Kathryn F. LaNoue, David Bassett, and John R . Williamson
Mitochondria were prepared from homogenates of rat lungs by modification of standard techniques. The mitochondrial preparation was characterized by its content of cytochromes, adenine and pyridine nucleotides, coenzyme A, and divalent cations. Rates of substrate oxidation were measured polarographically. Succinate was oxidized at a rate of 53 i 9 nmol of 02/min per mg of protein while other substrates were oxidized less rapidly. The C a ? + content of the mitochondrial preparation was of major importance in determining rates of substrate oxidation. Addition of 100-200 p~ Ca2+ during oxidation of NAD-linked substrates markedly decreased respiration rate; this effect was due to loss of free pyridine nucleotides from the mitochondria in the presence of Ca2+. On the other hand, very low levels of Ca2- (
