SUBCELLULAR ORGANIZATION OF INTERMEDIARY METABOLISM IN THE HEPATOPANCREAS OF THE TERRESTRIAL SNAIL, CEPAEA-NEMORALIS - A CYTOSOLIC BETA-HYDROXYBUTYRATE DEHYDROGENASE

The subcellular distributions of key enzymes of the tricarboxylic acid cycle, electron transport chain, ketone body, amino acid, and carbohy drate metabolism were studied in the hepatopancreas of the terrestrial snail Cepaea nemoralis. The presence of mitochondrial carnitine octan oyl transferase, carnitine palmitoyl transferase, and 3-hydroxyacyl-Co A dehydrogenase indicate an active lipid catabolic pathway in this tis sue. Activities of enzymes of ketone body metabolism are similar in ma gnitude to those of carbohydrate metabolism, suggesting an important m etabolic role for ketone bodies in C. nemoralis. Two enzymes that, in mammals, catalyze the synthesis of ketone bodies, hydroxymethylglutary l-CoA synthase and hydroxymethylglutaryl-CoA lyase, are not detectable in Cepaea hepatopancreas. The activity of 3-oxoacid-CoA transferase a nd a portion of acetoacetyl-CoA thiolase activity are found in the mit ochondria. beta-hydroxybutyrate dehydrogenase is a cytosolic enzyme in this tissue, and preferentially oxidizes the L-isomer of beta-hydroxy butyrate. A portion of glutamate dehydrogenase activity is also cytoso lic. The subcellular organization distribution of enzymes of intermedi ary metabolism in Cepaea hepatopancreas suggests adaptation to periodi c anoxia. (C) 1996 Wiley-Liss, Inc.