- The N-terminal membrane domain of yeast NADPH-cytochrome P450 (CYP) oxidoreductase is not required for catalytic activity in sterol biosynthesis or in reconstitution of CYP activity. Venkateswarlu, K., Lamb, D.C., Kelly, D.E., Manning, N.J., Kelly, S.L. J. Biol. Chem. (1998)