Pressure-adaptive differences in NAD-dependent dehydrogenases of congeneric marine fishes living at different depths

Abstract

The pressure sensitivities of the apparent Michaelis constant of coenzyme were compared at 5°C for three NAD-dependent dehydrogenases purified from the white muscle of two congeneric fishes living at different depths.Sebastolobus altivelis adults are common between 550 and 1,300 m;S. alascanus adults between 180 and 440 m. Two isozymes of cytoplasmic malate dehydrogenase (MDH, EC 1.1.1.37, NAD+:l-malate oxidoreductase) and glyceraldehyde 3-phosphate dehydrogenase (GAPDH, EC 1.2.1.12, NAD+:d-glyceraldehyde 3-phosphate oxidoreductase [phosphorylating]) were compared. For these enzymes, the homologues fromS. alascanus were markedly sensitive to moderate hydrostatic pressures (Fig. 1). TheK m(NADH) ofS. alascanus MDH-1 and theK m(NAD+) ofS. alascanus GAPDG double between 1 and 68 atm and continue to increase at a slower rate up to 476 atm, the highest pressure tested. For MDH-2 ofS. alascanus, theK m(NADH) triples between 1 and 68 atm and increases at a slower rate to 340 atm; between 340 and 476 atm, theK m decreases slightly from the value at 340 atm. TheK m of coenzyme values are pressure-independent for the MDH-1 and GAPDH homologues ofS. altivelis up to 476 atm (Fig. 1). TheK m(NADH) of theS. altivelis MDH-2 is sensitive to pressure, but much less so than the homologue ofS. alascanus (Fig. 1). TheK m increases 63% between 1 and 68 atm and remains constant at this higher value at higher pressures up to 476 atm. The relative increases inK m values for theS. alascanus enzymes between 1 and 68 atm are large (Table 1). Higher pressures are not as effective in perturbing theK m of coenzyme values. Perturbation ofK m of coenzyme by moderate hydrostatic pressures (50–100 atm) may seriously impair the function of dehydrogenases ofS. alascanus at pressures experienced by the deeper-living congener in its habitat. The reduction of the pressure-sensitivity of theK m of coenzyme in NAD-dependent dehydrogenases may be an important and ubiquitous feature of adaptation to the deep sea.