The effects of heme modification on reactivity, ligand binding properties and iron-coordination structures of cytochrome P450nor

Udai P. Singh, Eiji Obayashi, Satoshi Takahashi, Tetsutaro Iizuka, Hirofumi Shoun, Yoshitsugu Shiro

研究成果: Article査読

28 被引用数 (Scopus)

抄録

Artificial cytochrome P350nors (nitric oxide reductase) were prepared by replacing the native protoheme with various 4-substituted hemes: meso-, deutero-, and diacetyldeutero-hemes. For these samples, the ratio of low spin/high spin states of the ferric resting enzyme were varied, indicating that the coordination of the water molecule at the iron sixth site was affected by the electron withdrawing capacities of the heme 2,4-substituents. The binding of the water molecule reduces the rate of binding of nitric oxide (NO) to the ferric iron. In addition, the reduction reaction of the ferric-NO complex with NADH, which constitutes the second step in the NO reduction, was facilitated by the electron withdrawing capacity of 2,4-substituents. Consequently, proto- (native-) P450nor exhibited the highest overall enzymatic activity (NO reduction activity), while the enzymes containing diacetyl-, deutero-, and meso-hemes had considerably lower activities, since the NO reduction activity is determined by a balance of the reaction rates of the above two steps. The optical absorption spectra of the ferric-NO and the ferrous-CO complexes of the reconstituted enzymes show that the electron density on the heme in both states was modulated by the substituent groups. However, the resonance Raman spectral measurements showed that the Fc-NO and N-O stretching frequencies in the ferric-NO complex were insensitive to the electron density of the heme while the Fc-CO and C-O stretching frequencies in the ferrous-CO complex were sensitively varied by the electron withdrawing capacity of the 2,4-substituent. The differences are discussed in terms of the difference in the iron-ligand bond characters between the ferric-NO and the ferrous-CO complexes.

本文言語English
ページ(範囲)103-111
ページ数9
ジャーナルBiochimica et Biophysica Acta - Protein Structure and Molecular Enzymology
1384
1
DOI
出版ステータスPublished - 1998 4月 23
外部発表はい

ASJC Scopus subject areas

  • 生物理学
  • 構造生物学
  • 生化学
  • 分子生物学

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