Intracellular distribution of enzymes associated with lipogenesis and gluconeogenesis in fat body of the adult cockroach, Periplaneta

Abstract

The intracellular distribution and maximal activities of some enzymes associated with lipogenesis, gluconeogenesis and fatty acid oxidation have been determined in the fat body of the adult male cockroach Periplaneta americana. Of the enzymes of lipogenesis, acetyl-CoA synthase, acetyl-CoA carboxylase, glucose 6-phosphate dehydrogenase, and ATP citrate lyase are located entirely in the cytosol. Of the other enzymes of citrate metabolism studied, citrate synthase and NAD-dependent isocitrate dehydrogenase are almost exclusively mitochondrial, whereas NADP-dependent isocitrate dehydrogenase and aconitase are predominantly cytosolic although significant mitochondrial activity is also present. The latter subcellular distribution is also observed for ‘malic enzyme’ and NAD and NADP dependent malate dehydrogenase. The enzyme of fatty acid oxidation studied, 3-hydroxyacyl-CoA dehydrogenase is entirely mitochondrial. Of the enzymes possibly involved in gluconeogenesis, glucose 6-phosphate is microsomal, fructose 1,6-diphosphatase cytosolic, pyruvate carboxylase mitochondrial and phosphoenolpyruvate carboxykinase predominantly cytosolic. Of the enzymes of amino acid metabolism studied, glutamate dehydrogenase is NAD-dependent and located in the mitochondria whereas glutamate/oxalacetate and glutamate/pyruvate transaminases are predominantly cytosolic but with significant activity in the mitochondria. Glycerol kinase and sorbitol dehydrogenase are cytosolic and the glyoxylate cycle enzymes malate synthetase and isocitrate lyase are not detected in the fat body. The distribution and relative activities of the enzymes are discussed in relation to fat body biosynthesis and in comparison to mammalian liver and adipose tissue.