Effect of high pressure, detergents and phospholipase on the break in the Arrhenius plot of Azotobacter nitrogenase.

It is shown that lipids are responsible for the breaks in the Arrhenius plots of Azotobacter nitrogenase. The physical evidence is that temperature at which the break occurs increases with increasing pressure by 20 K/1000 atm. This is in agreement with the pressure dependence of the transition temperature of several synthetic phospholipids. We also find the same pressure dependence for the broad transitions observed in Escherichia coli phosphatidylethanolamine and in the membrane lipids from Azotobacter itself. Detergents and phospholipase remove the break. Reconstruction can be performed only with specific phospholipids.