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

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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, NAD+:l-malate oxidoreductase) and glyceraldehyde 3-phosphate dehydrogenase (GAPDH, EC, NAD+:d-glyceraldehyde 3-phosphate oxidoreductase [phosphorylating]) were compared. For these enzymes, the homologues from S. alascanus were markedly sensitive to moderate hydrostatic pressures (Fig. 1). The K m(NADH) of S. alascanus MDH-1 and the K m(NAD+) of S. 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 of S. alascanus, the K m(NADH) triples between 1 and 68 atm and increases at a slower rate to 340 atm; between 340 and 476 atm, the K m decreases slightly from the value at 340 atm. The K m of coenzyme values are pressure-independent for the MDH-1 and GAPDH homologues of S. altivelis up to 476 atm (Fig. 1). The K m(NADH) of the S. altivelis MDH-2 is sensitive to pressure, but much less so than the homologue of S. alascanus (Fig. 1). The K 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 in K m values for the S. alascanus enzymes between 1 and 68 atm are large (Table 1). Higher pressures are not as effective in perturbing the K m of coenzyme values. Perturbation of K m of coenzyme by moderate hydrostatic pressures (50-100 atm) may seriously impair the function of dehydrogenases of S. alascanus at pressures experienced by the deeper-living congener in its habitat. The reduction of the pressure-sensitivity of the K m of coenzyme in NAD-dependent dehydrogenases may be an important and ubiquitous feature of adaptation to the deep sea. © 1984 Springer-Verlag.

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Journal of Comparative Physiology B

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