Effect of Ethionine on Histidine Metabolism.

Summary Ethionine administration resulted in rapid and essentially complete inhibition of liver urocanase activity in the rat, while the activities of histidase and histidinepyruvate transaminase were relatively unaffected. Rats receiving ethionine in their diet, after showing a severe weight loss during the first week, resumed a rate of growth parallel to that of the control animals; there was, however, no restoration of urocanase activity during the period of adaptation to dietary ethionine. Thus, the straight deamination pathway for the degradation of histidine is not essential for the growth of the rat.