Kobayashi K, Hayashi K, Swallow A J
Institute of Scientific and Industrial Research, Osaka University, Japan.
Biochemistry. 1990 Feb 27;29(8):2080-4. doi: 10.1021/bi00460a017.
The reactions of the NAD radical (NAD.) with ferric horseradish peroxidase and with compounds I and II were investigated by pulse radiolysis. NAD. reacted with the ferric enzyme and with compound I to form the ferrous enzyme and compound II with second-order rate constants of 8 X 10(8) and 1.5 X 10(8) M-1 s-1, respectively, at pH 7.0. In contrast, no reaction of NAD. with native compound II at pH 10.0 nor with diacetyldeutero-compound II at pH 5.0-8.0 could be detected. Other reducing species generated by pulse radiolysis, such as hydrated electron (eaq-), superoxide anion (O2-), and benzoate anion radical, could not reduce compound II of the enzyme to the ferric state, although the methylviologen radical reduced it. The results are discussed in relation to the mechanism of catalysis of the one-electron oxidation of substrates by peroxidase.
通过脉冲辐解研究了NAD自由基（NAD.）与铁辣根过氧化物酶以及化合物I和II的反应。在pH 7.0时，NAD.与铁酶和化合物I反应分别形成亚铁酶和化合物II，二级速率常数分别为8×10⁸和1.5×10⁸ M⁻¹ s⁻¹。相比之下，在pH 10.0时未检测到NAD.与天然化合物II的反应，在pH 5.0 - 8.0时也未检测到与二乙酰氘代化合物II的反应。脉冲辐解产生的其他还原物种，如水合电子（eaq⁻）、超氧阴离子（O₂⁻）和苯甲酸根阴离子自由基，不能将酶的化合物II还原为铁态，尽管甲基紫精自由基可以将其还原。结合过氧化物酶催化底物单电子氧化的机制对结果进行了讨论。
