辣根过氧化物酶催化对香豆酸的羟基化反应。超氧自由基和羟基自由基的作用。

Hydroxylation of p-coumaric acid by horseradish peroxidase. The role of superoxide and hydroxyl radicals.

Halliwell B, Ahluwalia S

Biochem J. 1976 Mar 1;153(3):513-8. doi: 10.1042/bj1530513a.

Abstract

In the presence of dihydroxyfumarate, horseradish peroxidase catalyses the conversion of p-coumaric acid into caffeic acid at pH 6. This hydroxylation is completely inhibited by superoxide dismutase. 2. Dihydroxyfumarate cannot be replaced by ascorbate H2O2, NADH, cysteine or sulphite. Peroxidase can be replaced by high (10 mM) concentrations of FeSO4, but this reaction is almost unaffected by superoxide dismutase. 3. Hydroxylation by the peroxidase/dihydroxyfumarate system is completely inhibited by low concentrations of Mn2+ or Cu2+. It is proposed that this is due to the ability of these metal ions to react with the superoxide radical O2--. 4. Hydroxylation is partially inhibited by mannitol, Tris or ethanol and completely inhibited by formate. This seems to be due to the ability of these reagents to react with the hydroxyl radical -OH. 5. It is concluded that O2-- is generated during the oxidation of dihydroxyfumarate by peroxidase and reacts with H2O2 to produce hydroxyl radicals, which then convert p-coumaric acid into caffeic acid.

摘要

在二羟基富马酸存在的情况下，辣根过氧化物酶在pH 6时催化对香豆酸转化为咖啡酸。这种羟基化作用被超氧化物歧化酶完全抑制。2. 二羟基富马酸不能被抗坏血酸、H2O2、NADH、半胱氨酸或亚硫酸盐替代。过氧化物酶可以被高浓度（10 mM）的硫酸亚铁替代，但该反应几乎不受超氧化物歧化酶影响。3. 过氧化物酶/二羟基富马酸系统的羟基化作用被低浓度的Mn2+或Cu2+完全抑制。据推测，这是由于这些金属离子能够与超氧阴离子O2-反应。4. 羟基化作用被甘露醇、Tris或乙醇部分抑制，被甲酸盐完全抑制。这似乎是由于这些试剂能够与羟基自由基-OH反应。5. 得出的结论是，在过氧化物酶氧化二羟基富马酸的过程中会产生O2-，它与H2O2反应生成羟基自由基，然后羟基自由基将对香豆酸转化为咖啡酸。