Study of the Active Site Structure of Myeloperoxidase

髓过氧化物酶(MPO)是中性粒细胞抗菌系统的主要组成部分。尽管对该酶的光谱和酶性质进行了许多研究，但到目前为止还没有确定该酶的血红素基团的化学结构(铁卟啉与铁氯)1。在寻找MPO中血红素基团的合理模型的过程中，光原-Mb(PPPMb)是由去肌红蛋白和铁光原卟啉重组而成的。用光吸收、电子顺磁共振、共振拉曼光谱和磁圆二色谱研究了PPPMb衍生物的化学结构、电子结构和配体配位结构。PPPMb衍生物的可见光谱红移太远，使pPPMb不能成为很好的MPO模型。确定酶的底物结合部位对于进一步了解过氧化物酶催化反应的机理是非常重要的。我们测量了一些哺乳动物过氧化物酶的芳香底物络合物的EPR谱，以确定芳香底物结合对血红素铁的电子结构的影响。基于最近测定的MPO的三维结构建立的MPO-SHA(水杨基异羟肟酸)络合物的分子模型表明，芳香族底物分子的六元环可以结合到远端血红素口袋入口处的疏水区域。从MPO的活性部位结构可以了解其独特的生理功能。

Myeloperoxidase (MPO) is a major component of the antimicrobial system of polymorphonuclear neutrophils. Despite many investigations of the spectoscopic and exzymatic properties of this enzyme, the chemical structure of the heme group of this enzyme has not so far been identified (iron porphyrin vs iron chlorin).1. During the course of search for a plausible model for the heme group in MPO, photoproto-Mb (pPPMb) was reconstituted from apomyoglobin and iron photoprotoporphyrin. The chemical and electronic structure of the prosthetic group and the ligand coordination structure of pPPMb derivatives were studied by light absorption, EPR, resonance Raman and magnetic circular dichroism (MCD) spectroscopy. The pPPMb derivatives exhibit visible spectra too far "red-shifted" to make pPPMb a very good MPO model.2. It is important to identify the substrate binding site on the enzyme to further our understanding of the mechanism of the reaction catalyzed by peroxidase. We measured the EPR spectra of a number of aromatic substrate complexes of mammalian peroxidases to determine the effect of aromatic substrate binding upon the electronic structure of the heme iron. A molecular model for the MPO-SHA (salicylhydroxamic acid) complex based on the recently determined three dimensional structure of MPO indicated that the six-membered ring of aromatic substrate molecules could bind to a hydrophobic region at the entrance to the distal heme pocket. The distinct physiological function of MPO could be understood on the basis of its active site structure.