NADPH-cytochrome P-450 reductase. Circular dichroism and physical studies

NADPH-cytochrome P-450 reductase was purified from hepatic microsomes of phenobarbital and hydrocortisone-treated rats by detergent solubilization and column chromatography. This membrane protein contains 31 mol per cent hydrophobic amino acid residues, 6 half-cystine residues, and a single tryptophan residue as determined by amino acid analysis after mineral or organic acid hydrolysis. The free mobility of cytochrome P-450 reductase in sodium dodecyl sulfate was identical to that of several soluble proteins used as standards (i.e. ovalbumin, bovin serum albumin, erythrocuprein, beta-galactosidase). Molecular weight estimates from sedimentation equilibrium studies in the presence of guanidine hydrochloride (76,500) are consistent with those determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate at various per cent gel concentrations (79,000 to 80,000). Computer analysis of circular dichroism spectra of cytochrome P-450 reductase in the far ultraviolet region indicated the presence of 34 per cent alpha helical and 16 per cent beta structure. The amount of random structure was calculated to be 50 per cent.