The Effects of Nutritional and Hormonal Factors on the Fatty Acid Synthetase Level of Rat Liver

Abstract

Abstract The rise in fatty acid synthesizing capacity of the liver which is observed on realimentation of fasting rats with a fat-free diet has been studied. The rise to supranormal levels has been shown unequivocally to be the result of adaptive enzyme synthesis. Proof of this was obtained through the demonstration that 14C-leucine is readily incorporated in vivo into the purified fatty acid synthetase complex formed during refeeding. In addition, measurements of the absolute levels of the enzyme in the livers of fasting and refed rats showed drastic changes in the content of this protein complex with changes in nutritional status. Similarly, alloxan diabetic and portacaval-shunted rats exhibited lowered levels of fatty acid synthetase in liver; and insulin treatment of alloxan diabetic animals caused a return of the level of this enzyme toward the normal range. The characteristics of the fatty acid synthetase isolated from the livers of rats refed for varying periods of time after fasting have been investigated. Differences in homogeneity and variation in specific enzyme activity of these preparations were found which correlated with the length of time of refeeding. The significance of these variations is discussed.