Wakeham Marion C, Breton Jacques, Nabedryk Eliane, Jones Michael R
Department of Biochemistry, School of Medical Sciences, University of Bristol, University Walk, Bristol, BS8 1TD, United Kingdom.
Biochemistry. 2004 Apr 27;43(16):4755-63. doi: 10.1021/bi035726x.
In Rhodobacter sphaeroides reaction centers containing the mutation Ala M260 to Trp (AM260W), transmembrane electron transfer along the A-branch of cofactors is prevented by the loss of the QA ubiquinone. Reaction centers that contain this AM260W mutation are proposed to photoaccumulate the P(+)QB- radical pair following transmembrane electron transfer along the B-branch of cofactors (Wakeham, M. C., Goodwin, M. G., McKibbin, C., and Jones, M. R. (2003) Photoaccumulation of the P(+)QB- radical pair state in purple bacterial reaction centers that lack the QA ubiquinone. FEBS Lett. 540, 234-240). The yield of the P(+)QB- state appears to depend upon which additional mutations are present. In the present paper, Fourier transform infrared (FTIR) difference spectroscopy was used to demonstrate that photooxidation of the reaction center's primary donor in QA-deficient reaction centers results in formation of a semiquinone at the QB site by B-branch electron transfer. Reduction of QB by the B-branch pathway still occurs at 100 K, with a yield of approximately 10% relative to that at room temperature, in contrast to the QA- to QB reaction in the wild-type reaction center, which is not active at cryogenic temperatures. These FTIR results suggest that the conformational changes that "gate" the QA- to QB reaction do not necessarily have the same influence on QB reduction when the electron donor is the HB anion, at least in a minority of reaction centers.
在含有丙氨酸M260突变为色氨酸（AM260W）的球形红细菌反应中心中，QA泛醌的缺失阻止了沿辅因子A分支的跨膜电子转移。含有这种AM260W突变的反应中心被认为在沿辅因子B分支进行跨膜电子转移后光积累P(+)QB-自由基对（韦克姆，M.C.，古德温，M.G.，麦基宾，C.，和琼斯，M.R.（2003年）缺乏QA泛醌的紫色细菌反应中心中P(+)QB-自由基对状态的光积累。《欧洲生物化学学会联合会快报》540，234 - 240）。P(+)QB-状态的产率似乎取决于存在哪些其他突变。在本文中，傅里叶变换红外（FTIR）差示光谱法被用于证明在缺乏QA的反应中心中反应中心初级供体的光氧化通过B分支电子转移在QB位点形成半醌。与野生型反应中心中在低温下不活跃的QA到QB反应相反，通过B分支途径对QB的还原在100 K时仍然发生，相对于室温下的产率约为10%。这些FTIR结果表明，当电子供体是HB阴离子时，“控制”QA到QB反应的构象变化对QB还原不一定有相同的影响，至少在少数反应中心中是这样。
