Alteration of Tyrosine Aminotransferase Turnover in Rat Liver following Glucocorticoid Administration

Abstract

Abstract Tyrosine aminotransferase in adrenalectomized male rat liver was pulse labeled with uniformly labeled 14C-l-leucine. Biopsy samples from livers of control and hormone-treated animals were taken at intervals up to 8 hours following radioactive leucine administration. The specific radioactivity of tyrosine aminotransferase was measured by precipitating the enzyme with rabbit anti-tyrosine aminotransferase antiserum. Under basal conditions the half-time (t½) of tyrosine amino-transferase was determined to be 6.1 hours. This value is about 3½ times slower than inactivation of tyrosine amino-transferase following hormone induction (t½ = 1.7 hours). The apparent half-time of tyrosine aminotransferase during induction with triamcinolone was 11.7 hours. Total soluble liver protein had a t½ of about 75 to 84 hours when determined in a double labeling experiment with 14C-guanido-labeled l-arginine and 3H-l-leucine, respectively. Possible factors responsible for the relatively rapid rate of tyrosine aminotransferase turnover and its apparent alteration during and following hormone administration are discussed.