NUTRITIONAL AND HORMONAL REGULATION OF EXPRESSION OF THE GENE FOR MALIC ENZYME

Publisher Summary This chapter focuses on two lipogenic enzymes: malic enzyme and fatty-acid synthase. Malic enzyme catalyzes the oxidative decarboxylation of malate to pyruvate, simultaneously generating NADPH from NADP + . Fatty-acid synthase is a multifunctional polypeptide that catalyzes the final reactions in the synthesis of long-chain fatty acids. Macronutrients in the diet, or the products of their digestion in the gut, regulate the secretion of hormones that, in turn, regulate metabolic function in the liver and other organs. The humoral factors that regulate hepatic malic-enzyme activity during the transition between starved and fed states are identified in the chapter. Insulin stimulates and glucagon inhibits fatty-acid synthesis both in vivo and in isolated liver preparations. The activity of hepatic malic enzyme and hepatic lipogenesis are elevated in hyperthyroid animals and decreased in hypothyroid animals. The activity of an enzyme can be regulated by controlling the catalytic efficiency of that enzyme, for example, by allosteric mechanisms or covalent modifications.