Heme oxygenase: Active site structure studied by EPR of cobalt(II) porphyrin-enzyme complex

Abstract

Structure of the oxygen binding site in the heme complex of Heme Oxygenase (HO) has been elucidated by EPR (Electron Paramagnetic Resonance) spectroscopy of cobalt protoporphyrin IX complex of the enzyme. It has been found that the bound oxygen is hydrogen bonded to an amino acid residue in the heme pocket. The hydrogen bonding is favorable to the HO catalytic reaction because by decreasing the reduction potential of oxy HO. The hydrogen bonding also play a role in orienting the bound oxygen for the regiospecific hydroxylation at alpha-meso carbon of the porphyrin ring.

酵素のCoプロトポルフィリンIX複合体をEPR分光法(電子常磁性共鳴)で調べ、ヘムオキシゲナーゼ(HO)のヘム複合体内の酸素結合部位の構造を明らかにした。結合酸素はヘムポケット内のアミノ酸残基に水素結合していることを見出し、この水素結合はオキシHOの還元ポテンシャルを低減するためHO触媒反応に好ましく、またポルフィリン環のα-メソ炭素における位置特異的ヒドロキシル化に対して好ましい位置に結合酸素を配向する役割も果す。