title: Temperature and viscosity dependence of the electron-transfer reaction between plastocyanin and cytochrome c labeled with a ruthenium(II) bipyridine complex.
abstract: The temperature and viscosity dependence of the photo-induced electron-transfer reaction between plastocyanin and cytochrome c labeled at Lys13 with Ru(4,4'-dicarboxybipyridine)(bipyridine)(2+)2 have been investigated. In these studies, a short pulse of 450 nm light was used to excite the ruthenium complex which was oxidatively quenched by the iron center of cytochrome c. The resulting Fe(II) cytochrome c was then rapidly reoxidized by plastocyanin. The reactions were investigated over a temperature range of 3.5 to 37 degrees C under low ionic strength conditions such that protein/protein complex formation was favored. The enthalpy of activation was 7 kcal mol-1 and the entropy of activation was -20 cal mol-1 K-1. Increasing the viscosity by the addition of sucrose up to 70% resulted in a 4-fold decrease in the rate constant for electron transfer. The overall results suggest a rate-limiting step that involves either dissociation of the dominant protein/protein complex or surface diffusion of the associated proteins.
authors.affiliation: Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville 72701, USA.
authors.forename: M R
authors.initials: MR
authors.lastname: Harris
authors.forename: D J
authors.initials: DJ
authors.lastname: Davis
authors.forename: B
authors.initials: B
authors.lastname: Durham
authors.forename: F
authors.initials: F
authors.lastname: Millett
mesh_terms: D015082:2,2'-Dipyridyl / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D003574:Cytochrome c Group / Q000378:metabolism*; D004492:Edetic Acid / Q000494:pharmacology; D004579:Electron Transport; D006736:Horses; D007700:Kinetics; D008239:Lysine; D009206:Myocardium / Q000378:metabolism; D009942:Organometallic Compounds / Q000494:pharmacology*; D010782:Photolysis; D010970:Plastocyanin / Q000378:metabolism*; D011485:Protein Binding; D013053:Spectrophotometry; D013816:Thermodynamics; D014783:Viscosity
chemical_list: D003574:Cytochrome c Group; D009942:Organometallic Compounds; D015082:2,2'-Dipyridyl; C058014:ruthenium bis(bipyridine)dicarboxybipyridine; D010970:Plastocyanin; D004492:Edetic Acid; D008239:Lysine