Constraint on the substrate cytochrome [formula omitted] binding reaction in bovine adrenocortical microsomes at physiological temperature

Abstract

The addition of cholate to the microsomes at 37.5°C resulted in a striking decrease in the apparent substrate dissociation constant ( K′ s ) and its temperature dependency. The microsomal membranes depleted of 80% of the lipids preserved the temperature dependency of the K s and exhibited breaks in the Van't Hoff plot at the characteristic temperature of the lipids phase transition. The results indicate that the cytochrome P-450 is considerably restrained from expressing its maximum substrate binding potential at physiological temperature. In addition, the results indicate that the majority of the lipids apparently do not play a significant role in imposing constraint on the substratecytochrome P-450 binding reaction and in the temperature dependency of the K s .