PRESSURE ADAPTATION OF TELEOST GILL NA+/K+-ADENOSINE TRIPHOSPHATASE - ROLE OF THE LIPID AND PROTEIN MOIETIES

The effects of temperature and pressure on Na+/K+-adenosine triphosphatases (Na+/K+-ATPases) from gills of marine teleost fishes were examined over a range of temperatures (10-25°C) and pressures (1-680 atm). The relationship between gill membrane fluidity and Na+/K+-ATPase activity was studied using the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene (DPH). The increase in temperature required to offset the membrane ordering effects of high pressure was 0.015-0.025°C·atm-1, the same coefficient that applied to Na+/K+-ATPase activities. Thus, temperature-pressure combinations yielding the same Na+/K+-ATPase activity also gave similar estimates of membrane fluidity. Substituion of endogenous lipids with lipids of different composition altered the pressure responses of Na+/K+-ATPase. Na+/K+-adenosine triphosphatase became more sensitive to pressure in the presence of chicken egg phosphatidylcholine, but phospholipids isolated from fish gills reduced the inhibition by pressure of Na+/K+-ATPase. Cholesterol increased enzyme pressure sensitivity. Membrane fluidity and pressure sensitivity of Na+/K+-ATPase were correlated, but the effects of pressure also dependent on the source of the enzyme. Our results suggest that pressure adaptation of Na+/K+-ATPase is the result of both changes in the primary structure of the protein and homeoviscous adaptation of the lipid environment. © 1990 Springer-Verlag.