Effects of estrogen on the turnover rates of ornithine amino transferase in rat liver and kidney.

The turnover rates of ornithine aminotransferase in the liver and kidney of control rats and those treated with estrogen were determined by injecting L-[14C]leucine (U) and following the decay of specific radioactivity incorporated into immunoprecipitates from the partially purified enzymes. The half-life of the ornithine aminotransferase [EC 2.6.1.13] in the liver (t1/2=0.95 days) was significantly different from that of the kidney enzyme (t1/2=4.0 days). Studies on the incorporation of radioactive leucine into ornithine aminotransferase in the kidney under steady-state conditions showed that the rate of synthesis of this enzyme after treatment with estrogen was 5 to 6 times higher than that in untreated animals. The rate constant of degradation of kidney ornithine aminotransferase under steady-state conditions induced by estrogen treatment was not significantly different from that under control conditions. The results showed that the increase in the rate of biosynthesis, not to a decrease in the rate of degradation. No significant changes in the rates of biosynthesis and degradation of liver ornithine aminotransferase were observed after administration of estrogen.