Yamazaki I, Tamura M, Nakajima R
Mol Cell Biochem. 1981 Nov 13;40(3):143-53. doi: 10.1007/BF00224608.
Horseradish peroxidase C (HRP; ferric) reacts with H2O2 to form Compound I, with an equilibrium constant of about 10(14) M-1. Two-step reduction of Compound I to Compound II and further to the ferric enzyme occurs reversibly at Eo' values of 0.90 and 0.93 V (pH 7.0), respectively. The pH dependence of Eo' values for each one-electron step, ferrous leads to ferric leads to Compound II leads to Compound I indicates that presence of redox-linked ionization at pKa values of 7.3 in the ferrous state, 11.0 in the ferric and 8.6 in Compound II. Zinc-substituted HRP C is oxidized to its free-radical form at an Eo' value of 0.74 (pH 6.0) Comparison of oxidized zinc HRP C with Compound I shows that Compound I contains a porphyrin pi-cation radical. The flash photolysis study on the NO-ferric HRP C complex clearly indicates that the iron is pentacoordinated in HRP C while it is hexacoordinated in metmyoglobin. From the kinetic analysis of the acid-alkaline conversion of HRP C, the second-order rate constants of the reactions with H+ and HO- are estimated to be 1.5 X 10(10) and 6.7 X 10(4) M-1s-1, respectively. The latter rate constant greatly varies with the kind of hemoproteins. In the presence of HRP C and O2, indole-3-acetate is oxidized to its hydroperoxide form, which reacts effectively with HRP C to form Compound I and further converts Compound I to a verdohemoprotein.
辣根过氧化物酶C（HRP；铁离子形式）与过氧化氢反应生成化合物I，其平衡常数约为10(14) M-1。化合物I两步还原为化合物II并进一步还原为铁离子形式的酶，分别在Eo'值为0.90和0.93 V（pH 7.0）时可逆发生。每个单电子步骤的Eo'值对pH的依赖性，即亚铁离子转变为铁离子再到化合物II再到化合物I，表明在亚铁状态下pKa值为7.3、铁离子状态下为11.0、化合物II状态下为8.6时存在氧化还原相关的电离。锌取代的HRP C在Eo'值为0.74（pH 6.0）时被氧化为其自由基形式。氧化的锌HRP C与化合物I的比较表明，化合物I含有一个卟啉π-阳离子自由基。对NO-铁离子HRP C复合物的闪光光解研究清楚地表明，HRP C中的铁是五配位的，而在高铁肌红蛋白中是六配位的。通过对HRP C酸碱转化的动力学分析，与H+和HO-反应的二级速率常数估计分别为1.5×10(10)和6.7×10(4) M-1s-1。后一个速率常数随血红蛋白种类的不同而有很大变化。在HRP C和O2存在的情况下，吲哚-3-乙酸被氧化为其氢过氧化物形式，该形式与HRP C有效反应形成化合物I，并进一步将化合物I转化为高铁血红素蛋白。
