期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1981
卷号：78
期号：11
页码：6724-6728
DOI：10.1073/pnas.78.11.6724
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Laser flash photolysis has been used to determine the second-order rate constants for the reduction of horse heart cytochrome c by the semiquinone and fully reduced forms of various flavin analogs. We find that substitution in the dimethylbenzene ring of the flavin causes appreciable changes in the rate constants, whereas substitutions at the N-10 position do not. Placing a charged phosphate group in the N-10 ribityl side chain leads to only small ionic strength effects on the rate constants, whereas a charged group attached to the dimethylbenzene ring produces a large ionic strength effect. These results can be accounted for by assuming that a productive collision between flavin and cytochrome involves an orientation that positions the aromatic ring--N-5 region of the flavin toward the heme crevice and the N-10--pyrimidine ring region away from it. Our observations have implications for mechanistic understanding of biological electron transfer reactions and are discussed in this context.
