Effect of a zwitterionic detergent on the state of aggregation and catalytic activity of cytochrome P-450LM2 and NADPH-cytochrome P-450 reductase.

Abstract

The zwitterionic detergent 3-(3-cholamidopropyl)-dimethylammonio-1-propanesulfonate (CHAPS) supports reconstituted cyclohexane hydroxylase activity of cytochrome P-450LM2 and NADPH-cytochrome reductase purified from phenobarbital-induced rabbit liver. Maximum activity (approximately 50% of that with phospholipid) was observed at 2 mM CHAPS. Inhibition took place at higher CHAPS, until at 20 mM CHAPS, no cyclohexane hydroxylase activity was observed. There was little denaturation of the two enzymes under these conditions. At 2 mM CHAPS, P-450LM2 was pentameric (Mr = 250,000) and reductase was dimeric (Mr = 139,500) by sedimentation equilibrium. P-450 was monomeric in 20 mM CHAPS. In addition, a stable complex between the two enzymes was not detected under conditions of maximum activity, even in the presence of saturating substrate. This confirms our previous conclusion that a stable complex between cytochrome P-450LM2 and NADPH-cytochrome P-450 reductase is not a prerequisite for reconstituted xenobiotic hydroxylation (Dean, W. L., and Gray, R. D. (1982) J. Biol. Chem. 257, 14679-14685). Difference spectra of ferric P-450LM2 revealed that below 5 mM CHAPS, the high spin form of the cytochrome was slightly stabilized, while higher CHAPS levels stabilized the low spin form. Monomeric P-450LM2 formed with 20 mM CHAPS catalyzed the hydroxylation of toluene by cumene hydroperoxide. Thus, the reason that monomeric cytochrome P-450LM2 was inactive in NADPH-supported hydroxylation may either be because the bound detergent blocked productive interaction of the cytochrome with reductase or the monomer may be intrinsically incapable of interaction with reductase.