Mechanism of reaction of myeloperoxidase with hydrogen peroxide and chloride ion
Mechanism of reaction of myeloperoxidase with hydrogen peroxide and chloride ion
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DOI：
10.1046/j.1432-1327.2000.01491.x
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发表时间：
2000-10-01
期刊：
影响因子：
--
通讯作者：
Dunford, HB
中科院分区：
文献类型：
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作者：
Furtmüller, PC;Obinger, C;Dunford, HB
髓过氧化物酶化合物I （MPO-I）与氯离子的反应被广泛认为是产生细菌吞噬后的杀灭剂。这一重要反应的两个速率常数的值以前已经发表过：4.7 x 10(6) M-1。s（-1）在25摄氏度测量[Marquez， L.A.和Dunford， H.B.(1995)]。化学，270,30434 -30140]，和2.5 × 10(4) M-1。s（-1）在15℃下[Furtmuller， P.G, Burner， U.和Obinger .（1998）生物化学37,17923-17930]。这篇论文是两个小组合作解决速率常数差异的结果。结果表明，由髓过氧化物酶（MPO）与过量过氧化氢生成的化合物I与氯化物的反应速率常数随氯化物浓度的增加而减小。1995年公布的速率常数是在较低的氯化物浓度范围内测量的；1998年的速率常数在一个更高的范围。因此，所观察到的化合物I在过氧化氢和氯离子存在下向天然酶的转化不能仅仅归因于单一的基本反应MPO-I + Cl- -> MPO + HOCl。符合实验数据的最简单的反应机理如下：[图]其中MPO-I-Cl-是氯化中间体。我们现在可以说1995年的速率常数是k(2)，相应的反应是在低[Cl-]下控制速率的。在高[Cl-]时，反应速率常数为k(3)。1998年高[Cl-]的速率常数是一个复合速率常数，近似为k(2)k(3)/k(-2) k(1)和k（-1）的值从文献中已知。本研究的结果为k(2) = 2.2 x 10(6) M-1。s(-1) k(-2) = 1.9 x 10(5) s（-1）和k(3) = 5.2 x 10(4) s（-1）使用人髓过氧化物酶和牛肉脾髓过氧化物酶获得基本相同的结果。
The reaction of myeloperoxidase compound I (MPO-I) with chloride ion is widely assumed to produce the bacterial killing agent after phagocytosis. Two values of the rate constant for this important reaction have been published previously: 4.7 x 10(6) M-1.s(-1) measured at 25 degrees C [Marquez, L.A. and Dunford, H.B. (1995) J. Biol. Chem. 270, 30434-30140], and 2.5 x 10(4) M-1.s(-1) at 15 degrees C [Furtmuller, P.G., Burner, U. & Obinger, C. (1998) Biochemistry 37, 17923-17930]. The present paper is the result of a collaboration of the two groups to resolve the discrepancy in the rate constants. It was found that the rate constant for the reaction of compound I, generated from myeloperoxidase (MPO) and excess hydrogen peroxide with chloride, decreased with increasing chloride concentration. The rate constant published in 1995 was measured over a lower chloride concentration range; the 1998 rate constant at a higher range. Therefore the observed conversion of compound I to native enzyme in the presence of hydrogen peroxide and chloride ion cannot be attributed solely to the single elementary reaction MPO-I + Cl- --> MPO + HOCl. The simplest mechanism for the overall reaction which fit the experimental data is the following:[GRAPHICS]where MPO-I-Cl- is a chlorinating intermediate. We can now say that the 1995 rate constant is k(2) and the corresponding reaction is rate-controlling at low [Cl-]. At high [Cl-], the reaction with rate constant k(3) is rate controlling. The 1998 rate constant for high [Cl-] is a composite rate constant, approximated by k(2)k(3)/k(-2) Values of k(1) and k(-1) are known from the literature. Results of this study yielded k(2) = 2.2 x 10(6) M-1.s(-1) k(-2) = 1.9 x 10(5) s(-1) and k(3) = 5.2 x 10(4) s(-1) Essentially identical results were obtained using human myeloperoxidase and beef spleen myeloperoxidase.