Lipid modulation of the activity and temperature dependence of the purified (Na+ + Mg2+)-ATPase from Acholeplasma laidlawii B membranes.

The influence of lipid composition on the activity and temperature dependence of the purified (Na+ + Mg2+)-ATPase from Acholeplasma laidlawii B membranes has been investigated. The reconstituted enzyme requires liquid-crystalline lipid for full activity. However, phosphatidylcholines with fatty acids varying considerably in chemical structure and chain length all support comparable levels of activity at temperatures above their gel to liquid-crystalline phase transition temperatures, indicating that the specific activity of this ATPase is not dependent on membrane lipid fluidity. Phosphatidylethanolamines also effectively reconstitute this enzyme but anionic phospholipids do not, and in fact inhibit enzyme activity when mixed with zwitterionic phospholipids. The incorporation of cholesterol into phosphatidylcholine vesicles had no effect on ATPase activity except at high concentrations, where some inhibition occurs. Cholesterol also affects the temperature dependence of this enzyme somewhat, probably through its effect on the phase state of the phospholipids.