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首页> 外文期刊>Biochemistry >Constraints on the Radical Cation Center of Cytochrome c Peroxidase for Electron Transfer from Cytochrome c
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Constraints on the Radical Cation Center of Cytochrome c Peroxidase for Electron Transfer from Cytochrome c

机译：细胞色素c过氧化物酶的自由基阳离子中心对电子从细胞色素c转移的限制

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The tryptophan 191 cation radical of cytochrome c peroxidase (CcP) compound I (Cpd I) mediates long-range electron transfer (ET) to cytochrorne c (Cc). Here we test the effects of chemical substitution at position 191. CcP W191Y forms a stable tyrosyl radical upon reaction with peroxide and produces spectral properties similar to those of Cpd I but has low reactivity toward reduced Cc. CcP W191G and W191F variants also have low activity, as do redox ligands that bind within the W191G cavity. Crystal structures of complexes between Cc and CcP W191X (X = Y, F, or G), as well as W191G with four bound ligands reveal similar 1:1 association modes and heme pocket conformations. The ligarids display structural disorder in the pocket and do not hydrogen bond to Asp235, as does Trp191. Well-ordered Tyr191 directs its hydroxyl group toward the porphyrin ring, with no basic residue in the range of interaction. CcP W191X (X = Y, F, or G) variants substituted with zinc-porphyrin (ZnP) undergo photoinduced ET with Cc(III). Their slow charge recombination kinetics that result from loss of the radical, center allow resolution of difference spectra for the charge-separated state [ZnP+, Cc(II)]. The change from a phenyl moiety at position 191 in W191F to a water-filled cavity in W191G produces effects on ET rates much weaker than the effects of the change from Trp to Phe. Low net reactivity of W191Y toward Cc(II) derives either from the inability of ZnP or the Fe-CcP ferryl to oxidize Tyr or from the low potential of the resulting neutral Tyr radical.
机译：细胞色素c过氧化物酶（CcP）化合物I（Cpd I）的色氨酸191阳离子自由基介导向电子载体c（Cc）的远程电子转移（ET）。在这里，我们测试了位置191处化学取代的作用。CcPW191Y与过氧化物反应后形成稳定的酪氨酰自由基，并产生类似于Cpd I的光谱性质，但对还原的Cc具有较低的反应活性。 CcP W191G和W191F变体以及结合在W191G腔内的氧化还原配体也具有较低的活性。 Cc和CcP W191X（X = Y，F或G）之间的复合物的晶体结构，以及具有四个结合配体的W191G，都显示出相似的1：1缔合模式和血红素口袋构象。糖脂在口袋中显示出结构紊乱，并且不像Trp191那样氢键结合到Asp235上。有序的Tyr191将其羟基引导至卟啉环，在相互作用范围内没有碱性残基。用锌卟啉（ZnP）取代的CcP W191X（X = Y，F或G）变体与Cc（III）进行光诱导的ET。由于自由基中心的丢失而导致的缓慢的电荷重组动力学，使得分辨出了电荷分离态[ZnP +，Cc（II）]的不同光谱。从W191F位置191的苯基部分到W191G充满水的腔的变化，对ET速率的影响要比从Trp变为Phe的变化要弱得多。 W191Y对Cc（II）的净反应性低是由于ZnP或Fe-CcP茂铁无法氧化Tyr或所得中性Tyr自由基的电势低。

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