) Pergamon 0305-0491(94)E0027-Q Comp. Biochem. PhysioL Vol. 108B,No. 4, pp. 543-550, 1994 Copyright © 1994 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0305-0491/94$7.00 + 0.00 Lactate dehydrogenase, alanopine dehydrogenase and octopine dehydrogenase from the heart of Concholepas concholepas (Gastropoda: Muricidae) Nelson Carvajal, Edgardo Vega, Alejandro Erices, Daniel Bustos and Claudio Torres Departamento de Biologia Molecular, Facultad de Ciencias Biol6gicas, Universidad de Concepcirn, Casilla 152-C, Concepcirn, Chile Aianopine dehydrogenase, octopine dehydrogenase and lactate dehydrogenase activities were detected in the heart of C. concholepas. As determined by gel filtration on Sephadex G-100, the molecular weights (Mr) were 85,000, 42,000 and 52,000 for lactate dehydrogenase, alanopine dehydrogenase and octopine dehydrogenase, respectively. Substrate inhibition of the opine dehydrogenases was observed at high concentrations of both pyruvate and the corresponding amino acid (alanine or arginine). Moderate substrate inhibition of lactate dehydrogenase by pyruvate was observed; Km values for lactate and NAD ÷ were unusually high. Alanopine dehydrogenase was very specific for alanine and glycine was not a substrate for this enzyme. In addition to arginine, lysine was also a substrate for octopine dehydrogenase. Possible functions of the pyruvate reductases are discussed in connection with adaptation to anoxia and other regulatory processes in the heart of C. concholepas. Key words: Pyruvate reductase; Alanopine dehydrogenase; Octopine dehydrogenase; Lactate dehydrogenase; Heart; Gastropod heart; Concholepas concholepas; Mollusc enzymes. Comp. Biochem. Physiol. 108B, 543-550, 1994. Introduction We are studying the enzymatic aspects of the adaptive responses to anoxia in Conc- holepas concholepas. This marine gastropod inhabits the whole coast of Chile and southern Peril (Guisado and Castilla, 1983) and has the ability to withstand prolonged periods of environmental anoxia (Carvajal et al., 1990). Our interest has been focused on the enzymes involved in phospho- Correspondence to: N. Carvajal, Departamento de Biologia Molecular, Facultad de Ciencias Biolrg- icas, Universidad de Concepcirn, Casilla 152-C, Concepcirn, Chile. Received 7 September 1993; accepted 15 February 1994. enolpyruvate and pyruvate metabolism in tissues of C. concholepas. It is known that glycogen and aspartate are the fuels and succinate and alanine the major end-products of anaerobic metab- olism in anoxia-tolerant molluscs (G/ide, 1983). At the early stages of anoxia, there is a coupled conversion of glycogen to alanine and aspartate to succinate. When the aspar- tate reserves are exhausted, phospho- enolpyruvate is channelled, through the phosphoenolpyruvate-carboxykinase reac- tion, to the succinate pathway of glycogen degradation (G/ide, 1983; Eberlee and Storey, 1988; Michaelidis et al., 1988). The 543