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首页> 外文期刊>Biochemistry >AN ENGINEERED CATION SITE IN CYTOCHROME C PEROXIDASE ALTERS THE REACTIVITY OF THE REDOX ACTIVE TRYPTOPHAN
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AN ENGINEERED CATION SITE IN CYTOCHROME C PEROXIDASE ALTERS THE REACTIVITY OF THE REDOX ACTIVE TRYPTOPHAN

机译：细胞色素C过氧化物酶的工程化阳离子位点提高了氧化还原活性三甲酚的反应性

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The crystal structures of cytochrome c peroxidase and ascorbate peroxidase are very similar, including the active site architecture. Both peroxidases have a tryptophan residue, designated the proximal Trp, located directly adjacent to the proximal histidine heme ligand. During the catalytic cycle, the proximal Trp in cytochrome c peroxidase is oxidized to a cation radical. However, in ascorbate peroxidase, the porphyrin is oxidized, not the proximal Trp, despite the close similarity between the two peroxidase active site structures. A cation located approximate to 8 Angstrom from the proximal Trp in ascorbate peroxidase but absent in cytochrome c peroxidase is thought to be one reason why ascorbate peroxidase does not form a Trp radical. Site-directed mutagenesis has been used to introduce the ascorbate peroxidase cation binding site into cytochrome c peroxidase. Crystal structures show that mutants now bind a cation. Electron paramagnetic resonance spectroscopy shows that the cation-containing mutants of cytochrome c peroxidase no longer form a stable Trp radical. The activity of the cation mutants using ferrocytochrome c as a substrate is <1% of wild type levels, while the activity toward a small molecule substrate, guaiacol, increases. These results demonstrate that long range electrostatic effects can control the reactivity of a redox active amino acid side chain and that oxidation/reduction of the proximal Trp is important in the oxidation of ferrocytochrome c.
机译：细胞色素C过氧化物酶和抗坏血酸过氧化物酶的晶体结构非常相似，包括活性位点结构。两种过氧化物酶都具有色氨酸残基，称为色氨酸近端Trp，直接位于近端组氨酸血红素配体附近。在催化周期中，细胞色素c过氧化物酶中的近端Trp被氧化为阳离子自由基。但是，在抗坏血酸过氧化物酶中，尽管两个过氧化物酶活性位点结构之间具有相似的相似性，但卟啉被氧化，而不是近端Trp。位于抗坏血酸过氧化物酶中距Trp近端Trp约8埃但细胞色素C过氧化物酶中不存在的阳离子被认为是抗坏血酸过氧化物酶不能形成Trp自由基的原因之一。定点诱变已被用于将抗坏血酸过氧化物酶阳离子结合位点引入细胞色素c过氧化物酶。晶体结构表明突变体现在结合阳离子。电子顺磁共振光谱显示，细胞色素C过氧化物酶的含阳离子突变体不再形成稳定的Trp自由基。使用铁细胞色素c作为底物的阳离子突变体的活性小于野生型水平的1％，而对小分子底物愈创木酚的活性增加。这些结果表明，远距离静电效应可以控制氧化还原活性氨基酸侧链的反应性，并且近端Trp的氧化/还原在铁细胞色素c的氧化中很重要。

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