Regulation of d‐Triokinase and NAD‐Linked Glycerol‐Dehydrogenase Activities in Rat Liver

Abstract

The specific activities expressed as [μmol × g wet wt−1× min−1 of d‐triokinase and NAD‐linked glycerol dehydrogenase, with d‐glyceraldehyde as substrate, were determined in the 27500 ×g supernatant fraction of livers from rats subjected to various dietary and hormonal programs. The specific activity of triokinase varied over a three‐fold to four‐fold range, being lowest in livers of diabetic rats fed a Purina Chow and highest in livers of intact rats fed 72% fructose diets containing casein; total triokinase activity per liver was five‐fold to six‐fold greater in the latter group than in the former group. The specific activity of triokinase also increased in livers of rats fed diets of 72% glucose or 72% dextrin plus 18% casein. Fructose feeding caused a decrease in specific activity of glycerol dehydrogenase. Glucagon had no effect on the specific activity of either enzyme in livers of fasted rats. Cortisone tended to increase the specific activity of triokinase as well as its total activity in livers of rats fed the Purina Chow. After only 48 h of a 72% fructose‐18% casein diet, liver weight was increased 50% relative to livers of rats fed the Purina Chow. Triokinase is subject to regulation in livers of adult male rats. The data indicate that the NAD‐linked glycerol dehydrogenase is also subject to regulation but to a lesser extent. If glucagon does stimulate the flux of carbon in the triokinase or the NAD‐linked glycerol dehydrogenase reactions, it is not as the result of increases in enzyme concentrations as determined by assayable activity measurements. Copyright © 1972, Wiley Blackwell. All rights reserved