Effect of Hormones and Protein Level on Induction of Enzymes Involved in Histidine Degradation and Folate Metabolism

Abstract

Summary The effects of the hormones thyroxine, glucagon and hydrocortisone, and of protein level on hepatic histidase, urocanase, and certain folate enzymes were studied in rats. Hypothyroidism, induced either by feeding thiouracil or by thyroidectomy, increased histidase, urocanase, and the folate dependent enzyme formiminotransferase, and increased histidine metabolism as measured by oxidation of the 2-ring carbon of histidine to carbon dioxide. Hyperthyroidism, produced by feeding thyroid powder, decreased histidine oxidation and liver levels of this enzyme. Glucagon and hydrocortisone increased histidine oxidation and increased levels of histidase, urocanase and formiminotransferase. Elevated levels of casein and soy protein produced four to eight fold increases in histidase and urocanase, and 50% increases in formiminotransferase. Thus, increases in histidase and urocanase involved in the formation of formiminoglutamic acid (FIGlu) were accompanied by increases in the FIGlu metabolizing enzyme formiminotransferase.