Peroxidase-like activity of uncoupled cytochrome P450. Studies with Bilirubin and toxicological implications of uncoupling
de Matteis, Francesco and Ballou, D.P. and Coon, M.J. and Estabrook, R.W. and Haines, D.C. (2012) Peroxidase-like activity of uncoupled cytochrome P450. Studies with Bilirubin and toxicological implications of uncoupling. Biochemical Pharmacology 84 (3), pp. 374-382. ISSN 0006-2952.
The NADPH-dependent consumption of O2 by cytochrome P450 BM3 was stimulated by either laurate or perfluorolaurate, but the NADPH/O2 molar consumption ratios were approximately 1 and 2, respectively, indicating that perfluorolaurate does not become oxygenated by BM3 and oxygen undergoes full reduction to water. The nature of this catalytic cycle uncoupled to hydroxylation was explored using bilirubin as a molecular probe. During uncoupling with perfluorolaurate bilirubin was degraded and stimulated O2 uptake by an approximately equimolar amount. No stimulation of oxygen uptake was caused by bilirubin in presence of NADPH alone or in presence of laurate together with NADPH; under these conditions little degradation of bilirubin was observed. Mesobilirubin was also degraded during uncoupling with perfluorolaurate, whereas biliverdin (which lacks the central methene bridge present in rubins) was unaffected. It is suggested that the CYP ferryl oxygen species abstracts a hydrogen atom from the central methene bridge of bilirubin to generate a radical, which is further dehydrogenated to biliverdin or else binds O2 and undergoes fragmentation. We conclude that the uncoupled catalytic cycle of cytochrome P450 has properties resembling those of a peroxidase and that bilirubin is rapidly oxidized as a peroxidase substrate. The potential toxicological significance of Cytochrome P450 uncoupling is considered.
|Keyword(s) / Subject(s):||BM3, Cytochrome P450, Uncoupling, Perfluorolaurate, Bilirubin oxidation, NADPH/O2 consumption ratio|
|School:||Birkbeck Schools and Departments > School of Science > Biological Sciences|
|Date Deposited:||30 Apr 2012 14:41|
|Last Modified:||17 Apr 2013 12:23|
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