Araiso T, Miyoshi K, Yamazaki I
Biochemistry. 1976 Jul 13;15(14):3059-63. doi: 10.1021/bi00659a019.
Using a rapid-scan spectrophotometer equipped with a stopped-flow apparatus, reactions of sulfite with compounds I and II of two horseradish peroxidase isoenzymes A and C were investigated. The direct two-electron reduction of peroxidase compound I by sulfite occurred at acidic pH but the mechanism gradually changed to the two-step reduction with the intermediate formation of compound II as the pH increased. The pH at which the one- and two-electron changes occurred at the same speed was 4.5 for peroxidase A and 7.7 for peroxidase C. A new peroxidase intermediate was found in the reaction between peroxidase compound II and sulfite. The sulfite compound showed a characteristic absorption band at 850 nm and the optical spectrum was similar to that of isoporphyrins but was quite different from that of sulfhemoproteins. The rate (k) of conversion from the sulfite-compound II complex to the sulfite compound was proportional to the concentration of H+ and the log k vs. pH plot for peroxidase A moved to the acidic side by 1.1 pH unit from that for peroxidase C.
使用配备停流装置的快速扫描分光光度计，研究了亚硫酸盐与两种辣根过氧化物酶同工酶A和C的化合物I和II的反应。在酸性pH条件下，亚硫酸盐可直接将过氧化物酶化合物I双电子还原，但随着pH升高，反应机制逐渐转变为两步还原，并伴有化合物II中间体的形成。对于过氧化物酶A，单电子和双电子变化以相同速度发生时的pH为4.5；对于过氧化物酶C，则为7.7。在过氧化物酶化合物II与亚硫酸盐的反应中发现了一种新的过氧化物酶中间体。亚硫酸盐化合物在850 nm处呈现特征吸收带，其光谱与异卟啉相似，但与硫血红蛋白的光谱有很大不同。从亚硫酸盐 - 化合物II复合物转化为亚硫酸盐化合物的速率（k）与H⁺浓度成正比，过氧化物酶A的log k对pH曲线相对于过氧化物酶C向酸性方向移动了1.1个pH单位。
