Effects of Diet and Other Factors on Methionine Adenosyltransferase Levels in Rat Liver

Abstract

The effects of some nutritional and hormonal factors on the level of the activity of methionine adenosyltransferase in rat liver were studied with the following results: 1) Thyroidectomy and cortisone treatment increased the activity of this enzyme whereas adrenalectomy and administration of bovine growth hormone or triiodothyronine lowered its activity in the liver. 2) The activity also changed with dietary protein content. Intact animals fed a high protein diet had high activity but the adrenalectomized (or hypophysectomized) animals had low activities whatever the protein content of their diet. 3) Excess methionine added to a 27% casein diet caused little change in the activity. However, rats fed a protein-free diet supplemented with methionine or its 2-hydroxy analogue (but not glycine) retained a higher level of activity than those on the protein-free diet. 4) Starvation for 2 days brought about a decrease in the activity which returned to the normal level in the subsequent 2 days.