Effect of deuterium substitution on electron transfer at cytochrome c/SAM interfaces.
The involvement of protons in the heterogeneous electron transfer between cytochrome c and a gold electrode to which it is attached was studied by comparing the electron transfer rate constants for H2O and D2O solutions. Rate constants were measured as a function of the electrochemical cell solution and the protein incubant solution, i.e., k (0)(incubant, cell). Two separate isotope effects exist: a cell "isotope effect", KIE cell = k (0)(H2O, H2O): k (0)(H2O, D2O), which is manifest at short time scales (<30 s) and arises from the viscosity difference between H2O and D2O, and an incubant isotope effect, KIE inc= k (0)(H2O, H2O): k (0)(D2O, H2O), which is manifest at longer times (>2 h) and results from H/D exchange. The two isotope effects are approximately equal ( approximately 1.2) and a total isotope effect KIE total = k (0)(H2O, H2O): k (0)(D2O, D2O) can be constructed that is the product of KIE cell and KIE inc. The nature of the electron transfer process, possible coupling to a proton transfer process, and the involvement of specific hydrogens in the transfer mechanism are discussed.
Davis
Kathryn L
KL
Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260, USA.
Waldeck
David H
DH
D002021:Buffers; D045304:Cytochromes c / Q000737:chemistry* / Q000378:metabolism; D003903:Deuterium / Q000737:chemistry*; D017666:Deuterium Oxide / Q000737:chemistry; D004563:Electrochemistry; D004579:Electron Transport; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D012997:Solvents / Q000737:chemistry; D055672:Static Electricity; D013438:Sulfhydryl Compounds / Q000737:chemistry* / Q000378:metabolism; D013499:Surface Properties; D013997:Time Factors; D014783:Viscosity
D002021:Buffers; D012997:Solvents; D013438:Sulfhydryl Compounds; D045304:Cytochromes c; D003903:Deuterium; D017666:Deuterium Oxide