SULFENYLATION OF CYTOCHROMES P450 IN RESPONSE TO REDOX ALTERATION
Albertolle, Matthew Edward
Mammalian cytochrome P450 (P450) enzymes catalyze complex reactions involved in the biosynthesis of endogenous metabolites such as steroids, vitamins, and hormones. Additionally, several enzymes in this superfamily are involved in the metabolism of the majority of exogenous small molecule drugs. Advancing our understanding of P450 enzymes can lead to insights in cancer therapies (inhibiting hormone production), and to more precise pharmacokinetic and toxicologic prediction models for candidate drugs. Human P450s were tested to sensitivity to alterations in the reduction/oxidation (redox) environment. Results indicated that pretreatment of P450s 1A2, 2C8, 2D6, 3A4, and 4A11 with H2O2 led to a dose-dependent inhibition of the enzymes, while P450 1A2 was insensitive with up to 1 mM H2O2 pretreatment. To investigate the mechanism of this sensitivity, a chemoproteomic approach using isotope-coded dimedone/iododimedone was employed to selectively alkylate cysteine-sulfenic acids (-SOH) on the enzymes. It was discovered that the heme-thiolate cysteine ligand was sulfenylated in a H2O2 dose-dependent manner. This heme-thiolate sulfenylation was validated using spectroscopic techniques. Sulfenylation of P450s was also found to occur in mouse and human liver and kidney microsomes. These findings may play a role in disease-drug interactions where increases in drug metabolism half-lives have been observed in inflammatory diseases such as autoimmune disorders and influenza infection.