Verhagen M F, Meussen E T, Hagen W R
Department of Biochemistry, Agricultural University, Wageningen, The Netherlands.
Biochim Biophys Acta. 1995 May 11;1244(1):99-103. doi: 10.1016/0304-4165(94)00201-8.
The reduction potentials of bovine erythrocyte copper-zinc superoxide dismutase and Escherichia coli iron superoxide dismutase were determined in EPR-monitored redox titrations in homogeneous solution. The copper-zinc enzyme is reduced and reoxidized with a midpoint potential of +120 mV versus standard hydrogen electrode (SHE) at pH 7.5. The iron enzyme can be reduced with an apparent midpoint potential of -67 mV versus SHE at pH 7.5. However, reaction with ferricyanide affords only slow, partial re-oxidation. Cyclic voltammetry of the copper-zinc enzyme in the presence of 50 mM Sc3+ at pH 4.0 using a glassy carbon electrode results in asymmetric voltammograms. The midpoint potential of the enzyme at this pH value, calculated as the average of the anodic and cathodic peak potentials, is +400 mV versus SHE. The physiological relevance of this value is limited, since EPR experiments indicated that reduction of the copper-zinc enzyme at pH 4.0 is not reversible. Consequences of the irreversible behavior of the two dismutases for the previously reported studies on their redox properties are discussed.
在均相溶液中通过电子顺磁共振（EPR）监测的氧化还原滴定法测定了牛红细胞铜锌超氧化物歧化酶和大肠杆菌铁超氧化物歧化酶的还原电位。在pH 7.5时，铜锌酶的还原和再氧化的中点电位相对于标准氢电极（SHE）为 +120 mV。在pH 7.5时，铁酶可以以相对于SHE为 -67 mV的表观中点电位被还原。然而，与铁氰化物反应仅能缓慢地进行部分再氧化。在pH 4.0下，使用玻碳电极在50 mM Sc3+存在的情况下对铜锌酶进行循环伏安法测定，得到不对称的伏安图。在此pH值下，该酶的中点电位（计算为阳极和阴极峰电位的平均值）相对于SHE为 +400 mV。由于EPR实验表明在pH 4.0时铜锌酶的还原是不可逆的，所以该值的生理相关性有限。讨论了两种歧化酶的不可逆行为对先前报道的其氧化还原性质研究的影响。
