Redox properties of the Fe3+/Fe2+ couple in Arthromyces ramosus class II peroxidase and its cyanide adduct
Redox properties of the Fe3+/Fe2+ couple in Arthromyces ramosus class II peroxidase and its cyanide adduct
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DOI：
10.1007/s00775-006-0108-7
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发表时间：
2006-07-01
影响因子：
3
通讯作者：
Sola, Marco
中科院分区：
文献类型：
--
作者：
Battistuzzi, Gianantonio;Bellei, Marzia;Sola, Marco
通过光谱电化学实验，研究了植物过氧化物酶Arthromyces ramosus peroxidase（阿普）中亚铁血红素的单电子还原热力学。的数据进行了比较与III类辣根过氧化物酶C（HRP）和其氰化物加合物，并解释在配体结合功能，静电效应和溶剂的血红素基团和催化相关的残留物在血红素远端网站的可及表面积。游离ARP和氰化物结合ARP的E-o'值（在25 ℃和pH 7下分别为-0.183和-0.390 V）高于HRP和HRP-CN的E-o'值。阿普的特点是亚铁态的还原稳定和显着的负还原熵，这两个都是前所未有的血红素过氧化物酶。一旦从测量的还原焓中分离出溶剂重组的补偿性贡献，则所得的阿普的基于蛋白质的Δ H-rc（int）度的值比HRP的值少+10 kJ mol（-1）。较小的氧化血红素在阿普中的稳定性最可能是由于近端组氨酸的阴离子特征不太明显，以及与HRP相比血红素远端位点的极性降低，如X-射线结构所示。阿普的令人惊讶的负Δ S-rc度值是特殊的还原诱导的溶剂重组效应的结果。
The thermodynamics of the one-electron reduction of the ferric heme in free and cyanide-bound Arthromyces ramosus peroxidase (ARP), a class II plant peroxidase, were determined through spectro-electrochemical experiments. The data were compared with those for class III horseradish peroxidase C (HRP) and its cyanide adduct, and were interpreted in terms of ligand binding features, electrostatic effects and solvent accessible surface area of the heme group and of catalytically relevant residues in the heme distal site. The E-o' values for free and cyanide-bound ARP (-0.183 and -0.390 V, respectively, at 25 degrees C and pH 7) are higher than those for HRP and HRP-CN. ARP features an enthalpic stabilization of the ferrous state and a remarkably negative reduction entropy, which are both unprecedented for heme peroxidases. Once the compensatory contributions of solvent reorganization are partitioned from the measured reduction enthalpy, the resulting protein-based Delta H-rc(int)degrees' value for ARP turns out to be less positive than that for HRP by + 10 kJ mol(-1). The smaller stabilization of the oxidized heme in ARP most probably results from the less pronounced anionic character of the proximal histidine, and the decreased polarity in the heme distal site as compared with HRP, as indicated by the X-ray structures. The surprisingly negative Delta S-rc degrees' value for ARP is the result of peculiar reduction-induced solvent reorganization effects.