Research in progress is on the mechanism of adrenocortical microsomal hydroxylation reaction catalyzed by a cytochrome P-450 involved mixed function oxidase enzyme system. The aspects of the reaction currently being investigated are the role of phospholipids in (1) the binding of substrates to cytochrome P-450 and (2) the regulation of electron transport to the cytochrome. The studies involve resolution and reconstitution of the hydroxylase system. In addition they include experiments dealing with the effect of perturbation of the microsomal lipids on the membrane fluidity; substrate-cytochrome perturbation of the microsomal lipids on the membrane fluidity; substrate-cytochrome p-450 binding reaction and various aspects of the electron transport to the cytochrome in intact microsomal membranes as well as in the resolved and reconstituted system.