MITOCHONDRIAL PERMEABILITY AND ATPase ACTIVITY

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Abstract
The hydrolysis of ATP by isolated rat-liver mitochondria has been studied.It was found that gradual disorganization of mitochondrial structure had a biphasic action on ATPase activity similar to that of 2,4-dinitrophenol. Concomitantly a gradual appearance of the magnesium-activated ATPase and disappearance of the 2,4-dinitrophenol-activated ATPase was observed. The disorganization of mitochondria was obtained by preincubation or by treatment with Triton-X-100, n-butanol, oleic acid, or palmitic acid.The pH curves of ATPase activity in sucrose and in KCl media were found to have characteristics similar to those observed in swelling of mitochondria. The equilibrium of the magnesium-activated ATPase reaction depended upon the buffering power of the incubation medium. The activation of the "latent" ATPase by K+, Mg++, Mn++, and Ca++was studied.It is concluded that the "latency" of the ATPase of fresh mitochondria is due to accumulation of protons in the membrane. The removal of these protons by an increased permeability or by exchange with cations activates the "latent" ATPase.

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