Folkes L K, Candeias L P
Gray Laboratory Cancer Research Trust, Mount Vernon Hospital, Northwood, Middlesex, UK.
FEBS Lett. 1997 Jul 28;412(2):305-8. doi: 10.1016/s0014-5793(97)00792-8.
The catalytic cycle of heme peroxidases involves two reactive states, compound I and compound II. Although their reduction potentials at pH 7 are similar, compound I is in general more reactive towards organic substrates than compound II. The different reactivities have until now remained unexplained. In this study, the reactions of compounds I and II of peroxidase from horseradish with phenols were analyzed using the Marcus equation of electron-transfer. Both reactions exhibit similar reorganization energies, and the different reactivities of the two enzyme states can be ascribed to a higher apparent rate of activationless electron-transfer in the compound I reactions. This can be attributed to the shorter electron-tunneling distance on electron-transfer to the porphyrin radical cation in compound I, compared to electron-transfer to the iron ion in compound II.
血红素过氧化物酶的催化循环涉及两种活性状态，即化合物I和化合物II。尽管它们在pH 7时的还原电位相似，但化合物I通常比化合物II对有机底物的反应性更强。迄今为止，这种不同的反应性仍无法解释。在本研究中，利用电子转移的马库斯方程分析了辣根过氧化物酶的化合物I和化合物II与酚类的反应。两种反应都表现出相似的重组能，两种酶状态的不同反应性可归因于化合物I反应中更高的无活化能电子转移表观速率。这可归因于与化合物II中向铁离子的电子转移相比，化合物I中向卟啉自由基阳离子的电子转移的电子隧穿距离更短。
