Regulation of Tyrosine α-Ketoglutarate Transaminase in Rat Liver

The role of the pancreatic hormones, insulin and glucagon, in the regulation of hepatic tyrosine transaminase ( l -tyrosine:2-oxoglutarate aminotransferase, EC 2.6.1.5) was studied in adrenalectomized rats. Each of these hormones initiated a rapid but limited increase in the enzyme level, which reached a maximum after 2.5 to 3 hours. The optimal doses of insulin and glucagon per 100 g of body weight were 0.75 unit (33 µg) and 150 µg, respectively. Alloxan-induced diabetes in adrenalectomized rats caused a significant increase in the transaminase level after 5 days. Immunochemical-isotopic analyses showed that the pancreatic hormones cause an increase in the rate of transaminase synthesis which is comparable to that caused by hydrocortisone. Effects of the pancreatic hormones on the rate of enzyme synthesis are not additive with one another but are additive with the effect of hydrocortisone. Induction by either insulin or glucagon was inhibited by actinomycin D. A discrete mechanism for induction of this enzyme, which is steroid-independent and which can be initiated in vivo by either insulin or glucagon, is indicated.