Molecular oxygen oxidizes the porphyrin ring of the ferric α-hydroxyheme in heme oxygenase in the absence of reducing equivalent

Catharina Taiko Migita, Hiroshi Fujii, Kathryn Mansfield Matera, Satoshi Takahashi, Hong Zhou, Tadashi Yoshida

研究成果: Article査読

29 被引用数 (Scopus)

抄録

Heme oxygenase catalyzes the regiospecific oxidative degradation of iron protoporphyrin IX (heme) to biliverdin, CO and Fe, utilizing molecular oxygen and electrons donated from the NADPH-cytochrome P-450 reductase. The catalytic conversion of heme proceeds through two known heme derivatives, α-hydroxyheme and verdoheme. In order to assess the requirement of reducing equivalents in the second stage of heme degradation, from α-hydroxyheme to verdoheme, we have prepared the α-hydroxyheme complex with rat heme oxygenase isoform-1 and examined its reactivity with molecular oxygen in the absence of added electrons. Upon reaction with oxygen, the majority of the α-hydroxyheme in heme oxygenase is altered to a species which exhibits an optical absorption spectrum with a broad Soret band, along with the minority which is converted to verdoheme. The major product species, which is electron paramagnetic resonace-silent, can be recovered to the original α-hydroxyheme by addition of sodium dithionite. We have also found that oxidation of the α-hydroxyheme-heme oxygenase complex by ferricyanide or iridium(IV) chloride yields a species which exhibits an optical absorption spectrum and reactivity similar to those of the main product of the oxygen reaction. We infer that the oxygen reaction with the ferric α-hydroxyheme-heme oxygenase complex forms a ferric-porphyrin cation radical. We conclude that in the absence of reducing agents, the oxygen molecule functions mainly as an oxidant for the porphyrin ring and has no role in the oxygenation of α-hydroxyheme. This result corroborates our previous conclusion that the catalytic conversion of α-hydroxyheme to verdoheme by heme oxygenase requires one reducing equivalent along with molecular oxygen. Copyright (C) 1999 Elsevier Science B.V.

本文言語English
ページ(範囲)203-213
ページ数11
ジャーナルBiochimica et Biophysica Acta - Protein Structure and Molecular Enzymology
1432
2
DOI
出版ステータスPublished - 1999 7 13

ASJC Scopus subject areas

  • Biophysics
  • Structural Biology
  • Biochemistry
  • Molecular Biology

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