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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >Geminate carbon monoxide rebinding to a c-type haem
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Geminate carbon monoxide rebinding to a c-type haem

机译：萌芽的一氧化碳重新绑定到c型血红素

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摘要

A chemically modified form of cytochrome c (cyt.c),termed carboxymethyl cytochrome c (cm cyt.c),possesses a vacant sixth coordination site to the haem iron that is available to bind external ligands.We present data on the rapid flash photolysis of CO from the ferrous haem iron of cm cyt.c and describe the kinetics and spectral transitions that accompany the recombination.This was achieved using 30-femtosecond laser pulses and a white light continuum to monitor spectral transitions.Whereas the photo-dissociation quantum yield is close to 1,the yield of CO escape from the protein (the apparent quantum yield,phi) relative to myoglobin (phi=1) is small due to rapid geminate recombination of CO.On ligand photo-dissociation the haem undergoes a spin-state transition from low-spin ferrous CO bound to penta-coordinate high-spin.Subsequently the system reverts to the CO bound form.The data were fitted with a minimum number of exponentials using global analysis.Recombination of CO with the haem iron of cm cyt.c is multiphasic (tau=16 ps,120 ps and 1 ns),involving three spectrally distinct components.The fraction of haem (0.11) not recombining with CO within 4 ns is similar to the value of phi (0.12) measured on the same preparation by the "pulse method" (M.Brunori,G.Giacometti,E.Antonini and J.Wyman,Proc.Natl.Acad.Sci.USA,1973,70,3141-3144,ref.1).This implies that no further geminate recombination occurs at t > 4 ns.This unusually efficient CO-haem geminate recombination indicates the sterically hindered ("caged") nature of the distal haem pocket in cm cyt.c from which it is difficult for CO to escape.The large geminate phase may be contrasted with the behaviour of myoglobin in which geminate recombination is small.This is in general agreement with the well-documented extensive structural dynamics in myoglobin that allow ligand passage,and a higher structural rigidity in cyt.c imposed by the restraints of minimising reorganisation energy for electron transfer (M.Brunori,D.Bourgeois and D.Vallone,J.Struct.Biol,2004,147,223-234,ref.2).The high pH ferrous form of cm cyt.c is a low-spin species having a lysine bound to the central iron atom of the haem (M.Brunori,M.Wilson and E.Antonini,J.Biol.Chem.,1972,247,6076-6081;G.Silkstone,G.Stanway,P.Brzezinski and M.Wilson,Biophys.Chem.,2002,98,65-77,refs.3 and 4).This high pH (pH approx 8) form of deoxy cm cyt.c undergoes photo-dissociation of lysine (although the proximal histidine is possible) after photo-excitation.Recombination occurs with a time constant (tau) of approx 7 ps.This is similar to that observed for the geminate rebinding of the Met80 residue in native ferrous cyt.c (tau approx 6 ps) following its photo-dissociation (S.Cianetti,M.Negrerie,M.Vos,J.-L.Martin and S.Kruglik,J.Am.Chem.Soc.,2004,126,13 932-13 933;W.Wang,X.Ye,A.Demidov,F.Rosca,T.Sjodin,W.Cao,M.Sheeran and P.Champion,J.Phys.Chem.,2000,104,10789-10801,refs.5 and 6).
机译：化学修饰的细胞色素c（cyt.c）形式称为羧甲基细胞色素c（cm cyt.c）具有可与外部配体结合的血红素铁的空位第六配位位点。厘米cyt.c的亚铁血红素铁中的CO的变化，并描述了伴随重组的动力学和光谱跃迁，这是通过使用30飞秒激光脉冲和白光连续谱来监测光谱跃迁而实现的，而光解离量子产率接近1，由于CO的快速成对重组，相对于肌红蛋白（phi = 1），从蛋白质中逸出的CO的产率（表观量子产率phi）很小。配体光解时，血红素经历了自旋从低旋转的亚铁一氧化碳过渡到五坐标的高旋转状态，随后系统恢复为一氧化碳的结合形式，并使用全局分析将数据拟合为最小数量的指数。 cm cyt.c的铁是多相的（tau = 16 ps，120 ps和1 ns），涉及三个光谱上不同的成分。在4 ns内未与CO重组的血红素（0.11）的分数与phi（0.12）的值相似）是通过“脉冲法”（M.Brunori，G.Giacometti，E.Antonini和J.Wyman，美国国家科学院院刊，1973,70,3141-3144，ref.1）在同一制剂上测定的。 ）。这意味着在t> 4 ns时不会再发生geem重组。这种异常有效的CO-haem geem重组表明了cm cyt.c中远端haem口袋的空间受阻（“笼状”）性质，很难从中进行CO逃逸。大的萌芽期可能与肌红蛋白的行为形成鲜明对比，后者的萌芽重组很小。这与文献中广泛记载的肌红蛋白的广泛结构动力学（允许配体通过）和更高的细胞结构刚度一致.c受电子转移所需的重组能最小化的限制（M.Brunori，D.Bou rgeois and D.Vallone，J.Struct.Biol，2004,147,223-234，ref.2）.cm cyt.c的高pH亚铁形式是一种低自旋物种，其赖氨酸与Cy的中心铁原子结合。 haem（M.Brunori，M.Wilson和E.Antonini，J.Biol.Chem。，1972,247,6076-6081; G.Silkstone，G.Stanway，P.Brzezinski和M.Wilson，Biophys.Chem。， 2002,98,65-77，参考文献3和4）。这种高pH值（pH约为8）的脱氧cm cyt.c在光激发后经历了赖氨酸的光解离（尽管近端组氨酸是可能的）。发生时的时间常数（tau）约为7 ps，这与在光解离后天然亚铁cyt.c（tau约为6 ps）中Met80残基的发芽重结合所观察到的相似（S.Cianetti，M Negrerie，M.Vos，J.-L.Martin和S.Kruglik，J.Am.Chem.Soc。，2004,126,13 932-13933; W.Wang，X.Ye，A.Demidov，F Rosca T.Sjodin，W.Cao，M.Sheeran和P.Champion，J.Phys.Chem。，2000,104,10789-10801，参考文献5和6）。

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