SYNTHESIS AND DEGRADATION OF XANTHINE DEHYDROGENASE DURING CHICK LIVER DEVELOPMENT

Xanthine dehydrogenase is known to undergo a marked increase in activity in chick liver in the period after hatching. The increase in the specific activity of this enzyme has been confirmed in the present investigation. The enzyme was obtained in highly purified form from adult chick liver after a modification of the method of Rajagopalan and Handler (1967). Specific antiserum to the enzyme was used to measure the amount of enzyme protein from chicks 1-4 days old when there is at least a 3-fold increase in the specific activity of the enzyme. The results indicate that the increase in specific activity of the enzyme may be correlated with a similar increase in the amount of immunologically reactive protein. The rate of synthesis and of degradation of xanthine dehydrogenase was investigated by using uniformly labeled l-valine-14C. The labeled amino acid was injected at various times after hatching. The animals were sacrificed, livers were removed, and the enzyme was partially purified before precipitation with antiserum. The label incorporated into the enzyme after a brief 4-hour pulse provided an estimate of the rate of synthesis. The results indicate that the increase in specific activity of the enzyme may best be accounted for in terms of an increase in the rate of synthesis as well as a decrease in the rate of degradation at the early stages of development. © 1969.