Inactivation of NAD-dependent dehydrogenases from shallow- and deep-living fishes by hydrostatic pressure and proteolysis

Abstract

Cytoplasmic malate dehydrogenase (( l)-malate: NAD + oxidoreductase, EC 1.1.1.37) and glyceraldehyde-3-phosphate dehydrogenase ( d-glyceraldehyde-3-phosphate: NAD + oxidoreductase, EC 1.2.1.12) homologues from two shallow-living and three deep-living fishes were examined for the effects of hydrostatic pressure on enzyme activity and susceptibility to inactivation by proteinases. These studies were done to determine whether malate dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase homologues show similar patterns of adaptation to hydrostatic pressure as seen in lactate dehydrogenase ( l-lactate: NAD + oxidoreductase, EC 1.1.1.27) homologues from the same species (Hennessey, J.P., Jr. and Siebenaller, J.F. (1987) J. Exp. Zool. 241, 9–15). Fish malate dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase homologues are much less susceptible to inactivation by hydrostatic pressure than are lactate dehydrogenase homologues from the same species. This difference in susceptibility to inactivation by hydrostatic pressure may be due to the decreased number of intersubunit contacts in malate dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase homologues relative to lactate dehydrogenase homologues. Inactivation of malate dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase homologues by proteinases, both at atmospheric pressure and at elevated hydrostatic pressure, is less than for lactate dehydrogenase homologues from the same species. This suggests that the structural chracteristics and conformational perturbations that are responsible for the susceptibility of lactate dehydrogenase to proteolytic inactivation are not found in malate dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase homologues of the same species.