Turnover of Adenosine Triphosphatase from Rat Liver MitochondriaM

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Abstract
The half-life of mitochondrial ATPase and the relative rate constants of protein degradation for several fractions of rat liver was measured by the double-isotope technique. The apparent turnover rates of some mitochondrial enzymes, far apart in size, such as carbamoyl phosphate synthetase, glutamate dehydrogenase and malate dehydrogenase, are not related to MW or to size of subunits. In view of the possibility that mitochondrial proteins are degraded by different mechanisms, it was of interest to determine the half-life of a protein tightly bound to the inner membrane such as ATPase. The rate constants of degradation for rats fed a basal diet and injected at 3-day intervals with isotopic leucine were as follows: homogenate, Kd = 0.195 days-1; mitochondria, Kd = 0.135 days-1; cytosol, Kd = 0.140 days-1; microsomes, Kd = 0.28 days-1; ATPase, Kd = 0.275 days-1. The rate constants of the cellular fractions of liver of rats fed a high protein diet did not change or showed a small increase, compared with those of animals fed the basal diet, while those from rats on the protein-free diet showed a decrease. The rate constant for ATPase showed an increase with high-protein and a decrease with protein-free diet. A procedure for the purification of ATPase from a single liver of a rat is described.