Subcellular organization of intermediary metabolism in the hepatopancreas of the terrestrial snail,Cepaea nemoralis: A cytosolic β-hydroxybutyrate dehydrogenase

Abstract

The subcellular distributions of key enzymes of the tricarboxylic acid cycle, electron transport chain, ketone body, amino acid, and carbohydrate metabolism were studied in the hepatopancreas of the terrestrial snail Cepaea nemoralis. The presence of mitochondrial carnitine octanoyl transferase, carnitine palmitoyl transferase, and 3-hydroxyacyl-CoA dehydrogenase indicate an active lipid catabolic pathway in this tissue. Activities of enzymes of ketone body metabolism are similar in magnitude to those of carbohydrate metabolism, suggesting an important metabolic role for ketone bodies in C. nemoralis. Two enzymes that, in mammals, catalyze the synthesis of ketone bodies, hydroxymethylglutaryl-CoA synthase and hydroxymethylglutaryl-CoA lyase, are not detectable in Cepaea hepatopancreas. The activity of 3-oxoacid-CoA transferase and a portion of acetoacetyl-CoA thiolase activity are found in the mitochondria. β-hydroxybutyrate dehydrogenase is a cytosolic enzyme in this tissue, and preferentially oxidizes the L-isomer of β-hydroxybutyrate. A portion of glutamate dehydrogenase activity is also cytosolic. The subcellular organization distribution of enzymes of intermediary metabolism in Cepaea hepatopancreas suggests adaptation to periodic anoxia. © 1996 Wiley-Liss, Inc.