QUINONE BINDING SITES IN BACTERIAL REACTION CENTERS

细菌反应中心(RC)是一种膜结合蛋白，它 在转换电磁辐射中起着核心作用 转化为化学能。RC催化光驱电子 从细胞色素c2转移到苯醌-铁络合物，它含有 一种伯醌QA和一种次醌QB。初级阶段 苯二酚QA，在初始电子中起重要作用 转移步骤。次苯二酚QB在 电子和蛋白质的移位过程，起到两种作用 电子两种质子受体物种参与了 质子转移的第一步。这项建议解决了 苯二酚功能的分子基础问题 利用定点突变技术在细菌中的应用 RB。球形藻。通过修饰Q附近的氨基酸残基 结合位点和测量伴随的活性变化WE 将确定下列功能涉及的残留物： A)喹酮和除草剂的结合。苯二酚附近的残留物 结合位点会被修饰，对苯二酚的结合常数 除草剂将会被确定。结果将会给出 关于底物和抑制剂结合的性质的信息以及 除草剂抗性的机制。 B)电子转移动力学。芳香族和带电氨基酸 及其对电子传递的影响 下定决心。结果应该会提供有关 电子转移的机制。 C)QQ-的静电稳定。带电氨基酸 残留物将被修改，Q-A QB和QB之间的平衡 QAQ-B将被确定。结果应该会给出信息 关于膜蛋白质中的静电相互作用。 D)质子向QB的传输。可质子化残基，可以 潜在地形成从RC表面到RC表面的质子转移链 Qb位的修饰及其对质子速率的影响 转会将被决定。结果应该是对这种机制的检验 生物膜中质子传输的研究。

The bacterial reaction center (RC) is a membrane bound protein that plays the central role in the conversion lectromagnetic radiation into chemical energy. The RC catalyzes the light driven electron transfer from cytochrome c2 to a quinone-Fe complex, that contains a primary quinone QA and a secondary quinone QB. The primary quinone QA, plays an important role in the initial electron transfer step. The secondary quinone QB plays a central role in the electron and proteon translocation process, acting as a two electron two proton acceptor species which is involved in the primary step of proton translocation. This proposal addresses the question of the molecular basis for the function of the quinones using the technique of site directed mutagenesis in the bacterium Rb. sphaeroides. By modifying amino acid residues near the Q binding sites and measuring the concomitant changes in activity we will identify the residues involved in the following functions: a) Quinone and herbicide binding. Residues near the quinone binding sites will be modified and the binding constants of quinone and herbicide will be determined. The results will give information about the nature of substrate and inhibitor binding and the mechanism of herbicide resistance. b) Electron transfer kinetics. Aromatic and charged amino acids will be modified and their effects on electron tyransfer determined. The results should give information about the mechanisms of electron transfer. c) Electrostatic stabilization of QQ -. Charged amino acid residues will be modified and the equilibrium between Q-A QB and QAQ-B will be determined. The results should give information about the electrostatic interactions in a membrane protein. d) Proton transport to QB. Protonable residues which can potentialy form a proton transfer chain from the RC surface to the QB site will be modified and their effect on the rate of proton transfer will be detemined. The results should test the mechanism of proton transport in biological membranes.