Decrease of rat liver cysteine dioxygenase (cysteine oxidase) activity mediated by glucagon.

The hepatic cysteine dioxygenase activity of rats was markedly decreased by the intraperitoneal administration of glucagon. The enzyme activity was also decreased by either dibutyryl cyclic AMP or theophylline. The prior administration of actinomycin D completely blocked the glucagon-mediated decrease of enzyme activity, while administrations of this inhibitor of protein synthesis after glucagon injection did not block the decrease of enzyme activity. A single administration of actinomycin D resulted in a slight increase of cysteine dioxygenase activity in the rat liver. On the other hand, the injection of cycloheximide resulted in a rapid decrease of the hepatic cysteine dioxygenase with a half-life of 2.5 h. The half-life of the enzyme in rat liver after glucagon administration was one hour. The administration of hydrocortisone or insulin had no effect on the glucagon-mediated decrease of cysteine dioxygenase of rat liver. The enzyme activity of alloxan diabetic rat liver was almost the same as that of the intact rat liver. The evidence obtained here suggests that enhancement of degradation or inactivation of cysteine dioxygenase is responsible for the glucagon-mediated decrease of the enzyme activity in rat liver.