REACTION OF MYELOPEROXIDASE WITH ITS PRODUCT HOCL
REACTION OF MYELOPEROXIDASE WITH ITS PRODUCT HOCL
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DOI：
10.1111/j.1432-1033.1992.tb17097.x
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发表时间：
1992-07-15
期刊：
影响因子：
--
通讯作者：
WEVER, R
中科院分区：
文献类型：
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作者：
FLORIS, R;WEVER, R
采用快速扫描分光光度法和停流技术研究了人髓过氧化物酶与其产物次氯酸的反应。在髓过氧化物酶与次氯酸的反应中，发现一种与化合物I性质相似的初级化合物，该化合物转化为化合物II。主反应强烈依赖于ph值。在pH值为7.2时，反应速度太快，无法测量，但在较高的pH值下，可以确定表观二阶速率常数。其值减小到约2 × 10(7) M-1。在pH 8.3和2.3 （+/- 0.4）× 10(6) M-1。分别在pH 9.2下的s-1。在pH 9.2时，形成初级化合物的解离常数为25.7 (+/- 15.3)mu-M，在pH 8.3时，解离常数约为2.5 mu-M。化合物II的表观二级速率常数几乎不受pH的影响，在2 ~ 5 × 10(4) M-1之间变化。s-1分别在pH 10.2和pH 8.3下。髓过氧化物酶与次氯酸的反应也导致发色团不可逆的部分漂白。氯化物是该酶的底物，它不仅保护髓过氧化物酶免受次氯酸的漂白，而且竞争性地抑制次氯酸与髓过氧化物酶的结合，这一过程也在与过氧化氢的反应中被观察到。结论是次氯酸与血红素铁结合形成化合物I。
The reaction of human myeloperoxidase with its product, hypochlorous acid was investigated using both rapid-scan spectrophotometry and the stopped-flow technique. In the reaction of myeloperoxidase with hypochlorous acid a primary compound is found with properties similar to that of compound I and which is converted into compound II. The primary reaction is strongly pH-dependent. At pH 7.2 the reactions is too fast to be measured but at higher pH values it is possible to determine the apparent second-order rate constant. Its value decreases to about 2 x 10(7) M-1.s-1 at pH 8.3 and to 2.3 (+/- 0.4) x 10(6) M-1.s-1 at pH 9.2, respectively. The dissociation constant for the formation of the primary compound is 25.7 (+/- 15.3) mu-M at pH 9.2 and about 2.5-mu-M at pH 8.3. The apparent second-order rate constant for the formation of compound II is hardly affected by pH and varies between 2 to 5 x 10(4) M-1.s-1 at pH 10.2 and pH 8.3, respectively.Reaction of myeloperoxidase with hypochlorous acid also resulted in irreversible partial bleaching of the chromophore. Chloride, which is a substrate of the enzyme not only protects myeloperoxidase against bleaching by hypochlorous acid but also competitively inhibits the binding of hypochlorous acid to myeloperoxidase, a process which also has been observed in in the reaction with hydrogen peroxide. It is concluded that hypochlorous acid binds at the heme iron to form compound I.