title: Electron transfer in cytochrome c depends upon the structure of the intervening medium.
abstract: BACKGROUND
  Long-distance electron-transfer (ET) reactions through proteins are involved in a great many biochemical processes; however, the way in which the protein structure influences the rates of these reactions is not well understood. We have therefore measured the rates of intramolecular ET from the ferroheme to a bis(2,2'-bipyridine)imidazoleruthenium(III) acceptor at histidine 39 or 54 in derivatives of yeast iso-1-cytochrome c, and studied the effect of an asparagine to isoleucine mutation at position 52, a residue situated between the heme and the electron acceptor.
  
  
  RESULTS
  The Fe2+-->Ru3+ rate constants demonstrate that residue 52 affects ET from the heme to His54 (Ile52 > Asn52), but not to His39 (Ile52 = Asn52). The enhanced Fe(2+)-Ru3+(His54) electronic coupling for the N52I/K54H protein is in good agreement with sigma-tunneling calculations, which predict the length of the ET pathways between the heme and His54.
  
  
  CONCLUSIONS
  The structure of the intervening medium between the heme and electron acceptors at the protein surface influences the donor-acceptor couplings in cytochrome c.
authors.affiliation: Beckman Institute, California Institute of Technology, Pasadena 91125.
authors.forename: T B
authors.initials: TB
authors.lastname: Karpishin
authors.forename: M W
authors.initials: MW
authors.lastname: Grinstaff
authors.forename: S
authors.initials: S
authors.lastname: Komar-Panicucci
authors.forename: G
authors.initials: G
authors.lastname: McLendon
authors.forename: H B
authors.initials: HB
authors.lastname: Gray
mesh_terms: D001483:Base Sequence; D003574:Cytochrome c Group / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D045304:Cytochromes c; D004252:DNA Mutational Analysis; D004579:Electron Transport; D007700:Kinetics; D008956:Models, Chemical; D008958:Models, Molecular; D008969:Molecular Sequence Data; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D013053:Spectrophotometry
chemical_list: C014059:CYC1 protein, S cerevisiae; D003574:Cytochrome c Group; D029701:Saccharomyces cerevisiae Proteins; D045304:Cytochromes c