AGE-DEPENDENT DECREASE IN THE CYTOCHROME-C-OXIDASE ACTIVITY AND CHANGES IN PHOSPHOLIPIDS IN RAT-HEART MITOCHONDRIA

The effect of aging on the kinetic characteristics of cytochrome c oxi dase in rat heart mitochondria was investigated. Mitochondria from you ng and aged rats had equivalent K(m) values for cytochrome c, while th e maximal activity of the oxidase was significantly reduced in mitocho ndria from aged rats. The cytochrome aa3 content was the same in both these two types of mitochondria. The Arrhenius plot characteristics di ffer for cytochrome oxidase activity in mitochondria from aged rats as compared with young rats in that the breakpoint of the biphasic plot was shifted to a higher temperature. Cardiolipin content was markedly decreased in mitochondrial membrane from aged rats. No alterations wer e found in the patterns of the phospholipid fatty acid distribution of mitochondrial membranes from young and aged rats. The results support the conclusion that the reduced mitochondrial cytochrome c oxidase ac tivity in aged animals is due to a specific decrease in the cardiolipi n content.