Influence of age on thermotropic kinetics of enzymes involved in mitochondrial energy-metabolism.

Aging has recently been shown to promote lipid peroxidation of mitochondrial membranes by a mechanism involving chaotropic oxidants (5). The present paper reports on the relationship between these membrane alterations and the activities of lipid-dependent enzymes of isolated heart mitochondria from 3 month and 24 month old rats. 1. Temperature breaks of Arrhenius plots reveal age-dependent shifts to higher temperatures for the succinate oxidase system (delta t = 1,7 degrees C), the beta-hydroxybutyrate dehydrogenase, the succinate dehydrogenase and the ATP-ase (delta t = 3,0 degrees C). 2. Specific activities of the above enzymes are distinctly lowered in preparation from aged rats. 3. Thermotropic differences of the particular enzyme activities completely disappeared after solubilization of the lipid components by Triton X-100. 4. ESR studies exhibit a clear decrease in the fluidity of membrane lipids as a function of age. 5. Analysis of the membrane lipids by gas-liquid chromatography reveals a distinct age-dependent fall in the content of polyunsaturated fatty acids accompanied by a slow increase in the degree of fatty acid saturation. 6. It is concluded from the results that aging influences enzyme-protein-lipid interactions by radical-induced peroxidation of the surrounding membrane lipids, but does not affect the intrinsic properties of the membrane-bound enzymes themselves.