Effect of streptozotocin-induced diabetes mellitus on the turnover of rat liver pyruvate carboxylase and pyruvate dehydrogenase.

Immunochemical techniques were used to study the effect of streptozotocin-induced diabetes on the amounts of pyruvate carboxylase and pyruvate dehydrogenase and on their rates of synthesis and degradation. Livers from diabetic rats had twice the pyruvate carboxylase activity of livers from normal rats when expressed in terms of DNA or body weight. The changes in catalytic activity closely paralleled changes in immunoprecipitable enzyme protein. Relative rates of synthesis determined by pulse-labelling studies showed that the ratio of synthesis of pyruvate carboxylase to that of average mitochondrial protein was increased 2.0-2.5 times in diabetic animals over that of control animals. Other radioisotopic studies indicated that the rate of degradation of this enzyme was not altered significantly in diabetic rats, suggesting that the increase in this enzyme was due to an increased rate of synthesis. Similar experiments with pyruvate dehydrogenase, the first component of the pyruvate dehydrogenase complex, showed that livers from diabetic rats had approximately the same amount of immunoprecipitable enzyme protein as the control animals, but a larger proportion of the enzyme was in its inactive state. The rates of synthesis and degradation of pyruvate dehydrogenase were not affected significantly by diabetes.