KINETIC CHARACTERIZATION OF A CYTOSOLIC L-BETA-HYDROXYBUTYRATE DEHYDROGENASE FROM HEPATOPANCREAS OF A TERRESTRIAL SNAIL, CEPAEA-NEMORALIS

The hepatopancreas of the terrestrial gastropod Cepaea nemoralis has a cytoplasmic beta-hydroxybutyrate dehydrogenase specific for L-beta-hy droxybutyrate. No dehydrogenation of D-beta-hydroxybutyrate by the enz yme was detected under our experimental conditions. The apparent K-m f or L-beta-hydroxybutyrate is similar to K-m values for D-beta-hydroxyu butyrate determined for the mitochondrial D-beta-hydroxybutyrate dehyd rogenase from other sources. The apparent K-m for acetoacetate of the cytoplasmic L-beta-hydroxybutyrate dehydrogenase is an order of magnit ude greater than that of the mitochondrial enzyme. The cytosolic enzym e is markedly sensitive to pH, with opposite effects on V-max in the f orward and reverse directions. L-beta-hydroxybutyrate dehydrogenase ki netics are also affected by adenosine phosphates and acetoacetyl-CoA. The kinetic properties of the enzyme suggest that while L-beta-hydroxy butyrate dehydrogenation appears to be favoured, it could catalyze the production of L-beta-hydroxybutyrate from acetoacetate in the hepatop ancreas of estivating terrestrial snails. (C) 1997 Wiley Liss, Inc.