Pressure-adaptive differences in the binding and catalytic properties of muscle-type (M4) lactate dehydrogenases of shallow- and deep-living marine fishes
The pressure sensitivities of substrate (pyruvate) and cofactor (NADH) binding and catalytic rate of purified muscle-type (M4) lactate dehydrogenases (LDH, EC 126.96.36.199; NAD+: lactate oxidoreductase) from shallow- and deep-living teleost fishes were compared. The LDH's of the shallow species are significantly more pressure-sensitive than the LDH's of the deep-living fishes. The apparent Michaelis constant (Km)1 of pyruvate of the deep-living species' LDH's is pressure-insensitive over the entire pressure range used in these studies, 1 to 476 atmospheres (Fig. 1). For the LDH's of the shallow species, the Km of pyruvate increases significantly between 1 and 68 atmospheres, and then remains stable up to 476 atmospheres. The Km of NADH displays a much higher pressure sensitivity. For the LDH's of the deep species, the Km of NADH increases slightly (approximately 32%) between 1 and 68 atmospheres, and then remains stable up to 476 atmospheres (Fig. 1). The Km of the shallow species' LDH's rises sharply (approximately 113%) between 1 and 68 atmospheres, and then continues to increase at a slower rate up to 476 atmospheres. This marked inhibition of cofactor binding by pressure for the shallow species' LDH's may be of sufficient magnitude to seriously impair the function of these LDH's at pressures typical of those encountered by the deeper-living species. Pressure effects on optimal velocity, measured under high (optimal) concentrations of pyruvate and NADH, were generally lower for the LDH's of the deep species (Table 1). These results indicate that M4-LDH's of shallow water fishes are not pre-adapted for function at deepsea pressures, and that the reduction of pressure sensitivities of Km's and catalysis may be a ubiquitous feature of adaptation to life at depth. The virtually identical pressure responses of M4-LDH's from deepliving teleosts belonging to four different families represents a striking example of convergent evolution at the molecular level. © 1979, Springer-Verlag. All rights reserved.