Tollin G, Brown K, De Francesco R, Edmondson D E
Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322.
Biochemistry. 1987 Aug 11;26(16):5042-8. doi: 10.1021/bi00390a024.
Circular dichroism and 1H and 31P nuclear magnetic resonance spectroscopy have been used to investigate complex formation between cytochrome c and the flavodoxins from Azotobacter vinelandii and Clostridium pasteurianum. Such complexes are known to be involved in the mechanism of electron transfer between these two redox proteins. A large increase in ellipticity in the Soret band of the cytochrome heme was observed upon formation of the Clostridium flavodoxin complex, whereas much smaller changes were found for the complexes with either Azotobacter flavodoxin or an 8 alpha-imidazolyl-FMN-substituted Clostridium flavodoxin analogue. Similarly, the magnitudes of the perturbations of the contact-shifted heme proton resonances obtained upon complexation of cytochrome c by Azotobacter flavodoxin were much smaller than those previously shown for Clostridium flavodoxin [Hazzard, J. T., & Tollin, G. (1985) Biochem. Biophys. Res. Commun. 130, 1281-1286]. 31P nuclear magnetic resonance measurements were also consistent with differences in the interactions between the components in the complexes of the two flavodoxins with cytochrome c. It is suggested that these spectral changes are due to a loosening or opening of the heme crevice upon Clostridium flavodoxin binding, which allows closer contact between the heme and flavin prosthetic groups and results in a faster rate of electron transfer. The implications of these observations for biological oxidation-reduction processes are considered.
圆二色光谱法以及¹H和³¹P核磁共振光谱法已被用于研究细胞色素c与来自棕色固氮菌和巴氏芽孢梭菌的黄素氧还蛋白之间的复合物形成。已知此类复合物参与这两种氧化还原蛋白之间的电子转移机制。在形成巴氏芽孢梭菌黄素氧还蛋白复合物时，观察到细胞色素血红素的Soret带椭圆率大幅增加，而与棕色固氮菌黄素氧还蛋白或8α-咪唑基-FMN取代的巴氏芽孢梭菌黄素氧还蛋白类似物形成的复合物的变化则小得多。同样，棕色固氮菌黄素氧还蛋白与细胞色素c络合时获得的接触位移血红素质子共振的扰动幅度远小于先前报道的巴氏芽孢梭菌黄素氧还蛋白[哈扎德，J.T.，&托林，G.（1985年）生物化学与生物物理研究通讯130，1281 - 1286]。³¹P核磁共振测量结果也与两种黄素氧还蛋白与细胞色素c的复合物中各组分之间相互作用的差异一致。有人认为，这些光谱变化是由于巴氏芽孢梭菌黄素氧还蛋白结合后血红素裂隙变宽或打开，使得血红素与黄素辅基之间接触更紧密，从而导致电子转移速率加快。本文考虑了这些观察结果对生物氧化还原过程的影响。
