Matera K M, Takahashi S, Fujii H, Zhou H, Ishikawa K, Yoshimura T, Rousseau D L, Yoshida T, Ikeda-Saito M
Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106-4970, USA.
J Biol Chem. 1996 Mar 22;271(12):6618-24. doi: 10.1074/jbc.271.12.6618.
Heme oxygenase is a central enzyme of heme degradation and associated carbon monoxide biosynthesis. We have prepared the alpha-hydroxyheme-heme oxygenase complex, which is the first intermediate in the catalytic reaction. The active site structure of the complex was examined by optical absorption, EPR, and resonance Raman spectroscopies. In the ferric form of the enzyme complex, the heme iron is five coordinate high spin and the alpha-hydroxyheme group in the complex assumes a structure of an oxophlorin where the alpha-meso hydroxy group is deprotonated. In the ferrous form, the alpha-hydroxy group is protonated and consequently the prosthetic group assumes a porphyrin structure. The alpha-hydroxyheme group undergoes a redox-linked conversion between a keto and an enol form. The ferric alpha-hydroxyheme reacts with molecular oxygen to form a radical species. Reaction of the radical species with a reducing equivalent yields the verdoheme-heme oxygenase complex. Reaction of the ferrous alpha-hydroxyheme-heme oxygenase complex with oxygen also yields the verdoheme-enzyme complex. We conclude that the catalytic conversion of ferric alpha-hydroxyheme to verdoheme by heme oxygenase requires molecular oxygen and one reducing equivalent.
血红素加氧酶是血红素降解及相关一氧化碳生物合成的关键酶。我们制备了α-羟基血红素-血红素加氧酶复合物，它是催化反应中的首个中间体。通过光吸收、电子顺磁共振和共振拉曼光谱对该复合物的活性位点结构进行了研究。在酶复合物的铁离子形式中，血红素铁为五配位高自旋，复合物中的α-羟基血红素基团呈现出一种氧化卟啉结构，其中α-中位羟基去质子化。在亚铁离子形式中，α-羟基质子化，因此辅基呈现出卟啉结构。α-羟基血红素基团在酮式和烯醇式之间发生氧化还原相关的转化。高铁α-羟基血红素与分子氧反应形成一种自由基物种。该自由基物种与一个还原当量反应生成胆绿素-血红素加氧酶复合物。亚铁α-羟基血红素-血红素加氧酶复合物与氧反应也生成胆绿素-酶复合物。我们得出结论，血红素加氧酶将高铁α-羟基血红素催化转化为胆绿素需要分子氧和一个还原当量。
