Abstract
Kinetics of reduction of phototrophic bacterial flavocytochromes c by exogenous flavin semiquinones and fully reduced flavins generated by laser flash photolysis have been studied. The mechanisms of reduction of Chromatium and Chlorobium flavocytochromes c are more similar to one another than previously thought. Neither protein is very reactive with neutral flavin semiquinones (k less than 10(7) M-1 s-1), and the reactions with fully reduced flavins are slower than expected on the basis of comparison with other electron-transfer proteins of similar redox potentials. Deazaflavin radical is reactive with the flavocytochromes c by virtue of its low redox potential, but this reaction is also slower than expected on the basis of comparison with other electron-transfer proteins. These experiments indicate that the active site for reduction of flavocytochrome c is relatively buried and probably inaccessible to solvent. Fully reduced FMN does not show an ionic strength effect in its reaction with flavocytochrome c, which demonstrates that the active site is uncharged. Sulfite, which forms an adduct with protein-bound FAD, partially blocks heme reduction. This shows that heme is reduced via the FAD. The rate constant for intramolecular electron transfer between FAD and heme must be on the order of 10(4) s-1 or larger.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
