Heme oxygenase-1, intermediates in verdoheme formation and the requirement for reduction equivalents

Yi Liu, Pierre Moënne-Loccoz, Thomas M. Loehr, Paul R. Ortiz De Montellano

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103 Scopus citations


Conversion of heme to verdoheme by heme oxygenase-1 (HO-1) is thought to involve α-meso-hydroxylation and elimination of the meso-carbon as CO, a reaction supported by both H2O2 and NADPH-cytochrome P450 reductase/O2. Anaerobic reaction of the heme-HO-1 complex with 1 eq of H2O2 produces an enzyme-bound intermediate identified by spectroscopic methods as α- mesohydroxyheme. This is the first direct evidence for HO-1-catalyzed formation of α-meso-hydroxyheme. α-meso-Hydroxyheme exists as a mixture of Fe(III) phenolate, Fe(III) keto anion, and Fe(II) keto π neutral radical resonance structures. EPR shows that complexation with CO enhances the Fe(II) π neutral radical component. Reaction of the α-meso-hydroxyheme-HO-1 complex with O2 generates Fe(III) verdoheme, which can be reduced in the presence of CO to the Fe(II) verdoheme-CO complex. Thus, conversion of α- meso-hydroxyheme to Fe(III) verdoheme, in contrast to a previous report (Matera, K. M., Takahashi, S., Fujii, H., Zhou, H., Ishikawa, K., Yoshimura, T., Rousseau, D. L., Yoshida, T., and Ikeda-Saito, M. (1996) J. Biol. Chem. 271, 6618-6624), does not require a reducing equivalent. An electron is only required to reduce ferric to ferrous verdoheme in the first step of its conversion to biliverdin.

Original languageEnglish (US)
Pages (from-to)6909-6917
Number of pages9
JournalJournal of Biological Chemistry
Issue number11
StatePublished - Mar 14 1997

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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