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