Mechanism of nitrite-stimulated catalysis by lactoperoxidase.
Mechanism of nitrite-stimulated catalysis by lactoperoxidase.
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乳过氧化物酶亚硝酸盐刺激催化机制。
DOI：
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发表时间：
2001
期刊：
影响因子：
--
通讯作者：
P. Harvey
中科院分区：
文献类型：
--
作者：
T. Brück;R. J. Fielding;M. Symons;P. Harvey
研究了乳过氧化物酶(LPO)中间体化合物I、化合物II和化合物III与亚硝酸盐(NO2(-))的反应。化合物I被NO2(-)还原迅速(K2=2.3×10(-7)M(-1)x S(-1)；pH=7.2)，而化合物II不是中间体，说明当NO2(-)与化合物I反应时不产生NO2*。在pH=7.2条件下，化合物II与NO2(-)反应的二级速率常数为3.5×10(5)M(-1)x S(-1)。当观察到的准一级速率常数与NO2(-)浓度作图时，化合物III与NO2(-)的反应呈现饱和行为，并可用1：1比例的化合物III/NO2(-)络合物的形成来定量解释。化合物III对NO_2(-)的Km为1.7×10~(-4)M，化合物III/NO_2(-)络合物的一级衰减常数为12.5+/-0.6 S(-1)。该络合物与亚硝酸根反应的二级速率常数为3.3×10~(-3)M~(-1)×S~(-1)。NO2(-)的速率增强不需要NO2*作为氧化还原中间体。NO2(-)通过将化合物II还原到铁态来加快总的催化速度。随着过氧化氢水平的增加，催化死端中间体III的生成趋势增加。在此条件下，NO2(-)与化合物III的‘挽救’反应生成化合物II，将维持酶的过氧化循环。
The reactions of lactoperoxidase (LPO) intermediates compound I, compound II and compound III, with nitrite (NO2(-)) were investigated. Reduction of compound I by NO2(-) was rapid (k2 = 2.3 x 10(7) M(-1) x s(-1); pH = 7.2) and compound II was not an intermediate, indicating that NO2* radicals are not produced when NO2(-) reacts with compound I. The second-order rate constant for the reaction of compound II with NO2(-) at pH = 7.2 was 3.5 x 10(5) M(-1) x s(-1). The reaction of compound III with NO2(-) exhibited saturation behaviour when the observed pseudo first-order rate constants were plotted against NO2(-) concentrations and could be quantitatively explained by the formation of a 1 : 1 ratio compound III/NO2(-) complex. The Km of compound III for NO2(-) was 1.7 x 10(-4) M and the first-order decay constant of the compound III/ NO2(-) complex was 12.5 +/- 0.6 s(-1). The second-order rate constant for the reaction of the complex with NO2(-) was 3.3 x 10(3) M(-1) x s(-1). Rate enhancement by NO2(-) does not require NO2* as a redox intermediate. NO2(-) accelerates the overall rate of catalysis by reducing compound II to the ferric state. With increasing levels of H2O2, there is an increased tendency for the catalytically dead-end intermediate compound III to form. Under these conditions, the 'rescue' reaction of NO2(-) with compound III to form compound II will maintain the peroxidatic cycle of the enzyme.
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影响因子：
5.6
作者：
Putnam, CD;Arvai, AS;Tainer, JA
通讯作者：
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影响因子：
3.9
作者：
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通讯作者：
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影响因子：
2.9
作者：
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通讯作者：
Rahemtulla,F
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影响因子：
7.4
作者：
Reszka,KJ;Matuszak,Z;Chignell,CF;Dillon,J
通讯作者：
Dillon,J