Transient kinetics of redox reactions of flavodoxin: effects of chemical modification of the flavin mononucleotide prosthetic group on the dynamics of intermediate complex formation and electron transfer.
Transient kinetics of redox reactions of flavodoxin: effects of chemical modification of the flavin mononucleotide prosthetic group on the dynamics of intermediate complex formation and electron transfer.
复制标题
黄素氧还蛋白氧化还原反应的瞬态动力学：黄素单核苷酸辅基的化学修饰对中间复合物形成和电子转移动力学的影响。
DOI：
10.1021/bi00281a034
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发表时间：
1983
期刊：
影响因子：
2.9
通讯作者：
Tollin,G
中科院分区：
文献类型：
--
作者：
Simondsen,RP;Tollin,G
1976； Jung & Tollin, 1981) 以及其他文章 [有关优秀的评论，请参见 Massey & Hemmerich (1980)；另见 Claiborne 等人 (1982)]。各种取代和改性黄素的可用性为研究黄素功能的几乎各个方面提供了可能性。 X 射线晶体结构分析 (Mayhew & Ludwig, 1975)、早期的停流研究 (Shiga & Tollin, 1976; Jung & Tollin, 1981) 以及对假定的黄素氧还蛋白-细胞色素 C 电子转移复合物结构的计算机图形研究 (Simondsen 等人, 1982) 表明黄素环系统中部分暴露的二甲苯部分参与了黄素氧还蛋白的电子转移反应。从游离黄素半醌到细胞色素 c 的电子转移的激光闪光光解观察（Ahmad 等人，1981）也表明黄素的该区域与细胞色素的结合血红素辅基相互作用。目前的研究正是针对黄素结构/功能关系的这一方面。电子顺磁共振（EPR）和电子核双共振（ENDOR）光谱表明，二苯环中的8位在游离黄素和黄素氧还蛋白的半醌形式中携带大量不成对的自旋密度（Guzzo＆Tollin，1964；Er-iksson＆Ehrenberg， 1973）而 7 位则不然。这与8位参与半醌水平的电子转移是一致的。这种可能性的有效性可以通过单独取代这些位置上的甲基来研究。理想的取代基是氯，因为它对类似大小的甲基的取代可能不会因空间效应而导致蛋白质构象发生任何大的变化，而其高电负性应该会显着扰乱黄素的电子结构（Jung＆Tollin，1981）。两个都
1976; Jung & Tollin, 1981) as well as in others [for an ex-cellent review, see Massey & Hemmerich (1980); see also Claiborne et al.(1982)]. The availability of variously sub-stituted and modified flavins offers possibilities for studying virtually every aspect of flavin functionality. X-ray crystal structure analysis (Mayhew & Ludwig, 1975), earlier stop-ped-flow studies (Shiga & Tollin, 1976; Jung & Tollin, 1981), and a computer graphics investigation of the structure of a putative flavodoxin-cytochrome c electron-transfer complex (Simondsen et al., 1982) have suggested the involvement of the partially exposed dimethylbenzene moiety of the flavin ring system in electron-transfer reactions of flavodoxin. Laser flash photolysis observations (Ahmad et al., 1981) of electron transfer from free flavin semiquinone to cytochrome c also have implicated this region of the flavin in interactions with the bound heme prosthetic group of the cytochrome. It is to this aspect of flavin structure/function relationships that the present studies are directed.Electron paramagnetic resonance (EPR) and electron nu-clear double resonance(ENDOR) spectroscopies have indi-cated that the 8-position in the dimethylbenzene ring carries substantial unpaired spin density in the semiquinone forms of both free flavin and flavodoxin (Guzzo & Tollin, 1964; Er-iksson & Ehrenberg, 1973) whereas the 7-position does not. This would be consistent with the participation of the 8-position in electron transfer at the semiquinone level. The validity of this possibility may be investigated by individually substituting the methyl groups at these positions. An ideal substituent would be chlorine since its replacement of the similarly sized methyl group probably would not lead to any large changes in the conformation of the protein caused by steric effects, whereas its high electronegativity should significantly perturb the flavin electronic structure (Jung & Tollin, 1981). Both