Induction of Tyrosine-a-ketoglutarate Transamimase in Rat Liver

Previous papers of this series have demonstrated that induction of tyrosine oc-ketoglutarate transaminase of rat liver can be attributed to adrenocortical hormone (1) and described extensive purification of the transaminase from normal and induced livers (2). The present report describes experiments in which the induction phenomenon was analyzed with a highly specific antiserum prepared against the enzyme purified from induced livers. Analysis was directed toward determining whether the increase in activity observed on induction reflects a hormonal stimulation of specific enzyme synthesis or some other mechanism. In a preliminary report (3), the results of precipitin and labeling cxperiments were interpreted as suggesting the existence of an inactive precursor to the enzyme in the noninduced state. The present esperiments, in which a more specific antiserum and techniques for ensuring specificity in immunological assays have been used, confirm the preliminary observations reported, insofar as they demonstrate that enzyme labeling is independent of induction. However, the data also demonstrate that a simple precursorenzyme interconversion is not involved.