Turnover of hepatic mitochondrial ornithine aminotransferase and cytochrome oxidase using (14C)carbonate as tracer.

Abstract

Abstract The half-lives of the liver mitochondrial enzymes, ornithine aminotransferase (L-ornithine: 2-oxo acid aminotransferase, EC 2.6.1.13) and cytochrome oxidase (ferrocytochrome c : oxygen oxidoreductase, EC 1.9.3.1), have been determined under basal conditions by injecting rats with NaH 1 4 CO 3 and following the decay in specific radioactivity of arginine isolated from the purified enzymes. This technique gave half-lives for the two enzymes of 1.9 and 5.7 days, respectively. An identical half-life was obtained for cytochrome oxidase using δ-amino [ 3 H]levulinate as a tracer, thus indicating that the heme and apoprotein moieties of this enzyme turn over at the same rate. The degradation rate constant of ornithine aminotransferase under induced, steady-state conditions, i.e. in rats fed a diet containing 80% of casein, was not significantly different from that under basal conditions; hence, the increased amount of enzyme present under these conditions must be due to an increased rate of synthesis. Fractionation of mitochondria with digitonin and Lubrol WX, and comparison with marker enzymes, indicated that ornithine aminotransferase is located within the mitochondrial matrix.