Methionine metabolism in mammals: Effects of age, diet, and hormones on three enzymes of the pathway in rat tissues

Abstract

A comprehensive survey has been made to determine the effects of age, diet, and hormone administration on the activities of methionine-activating enzyme, cystathionine synthase, and cystathionase in rat tissues. Specific, sensitive assays were employed to measure changes in the levels of these enzymes in liver, kidney, pancreas, and brain. From these studies we concluded that (a) The developmental pattern of each enzyme varied in the several tissues and the patterns of the three enzymes often varied in the same tissue, (b) Many significant, organ-specific changes in the levels of individual enzymes can be effected by dietary and hormone treatments. However, these factors rarely resulted in a parallel change in the three enzymes in one organ or in a single enzyme in all organs, (c) The response of hepatic cystathionine synthase to many of these factors varies markedly from that observed for threonine dehydratase. This provides additional evidence that these two enzyme activities are not properties of a single protein in mammalian liver, (d) There are several possible implications of this study for the treatment of human cystathionine synthase deficiency (homocystinuria).