Swelling and Contraction of Corn Mitochondria

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Abstract
A survey was made of the properties of corn mitochondria in swelling and contraction. The mitochondria swelled spontaneously in KC1 but not in sucrose. Aged mitochondria swelled rapidly in sucrose if treated with citrate or EDTA. Swelling did not impair oxidative phosphorylation if bovine serum albumin was present. Contraction was maintained or initiated with ATP + Mg or an oxidizable substrate, contraction being more rapid with the substrate. M was not required for substrate powered contraction. Contraction powered by ATP was accompanied by the release of phosphate. Oligomycin inhibited both ATP-powered contraction and the release of phosphate. However, it did not affect substrate-powered contraction. Substrate powered contraction was inhibited by electron-transport inhibitors. The uncoupler, carbonyl cyanide m-chlorophenyl hydrazone, accelerated swelling and inhibited both ATP-and substrate-powered contraction. However, the concentrations required were well in excess of those required to produce uncoupling and to accelerate adenosine triphosphatase; the concentrations required inhibited respiration in a phosphorylating medium. Phosphate was a very effective inhibitor of succinate-powered contraction. Neither oligomycin nor Mg affected the phosphate inhibition. Phosphate was less inhibitory with the ATP-powered contraction. The results are discussed in terms of a hypothesis that contraction is associated with a nonphosphorylated energy intermediate of oxidative phosphorylation.