title: Activation volumes for intramolecular electron transfer in Escherichia coli cytochrome bo(3).
abstract: In this report we describe the activation volumes associated with the heme-heme electron transfer (ET) and CO rebinding to the binuclear center subsequent to photolysis of the CO-mixed-valence derivative of Escherichia coli cytochrome bo(3) (Cbo). The activation volumes associated with the heme-heme ET (k=1.2 x 10(5) s(-1)), and CO rebinding (k=57 s(-1)) are found to be +27.4 ml/mol and -2.6 ml/mol, respectively. The activation volume associated with the rebinding of CO is consistent with previous Cu X-ray absorption studies of Cbo where a structural change was observed at the Cu(B) site (loss of a histidine ligand) due to a change in the redox state of the binuclear center. In addition, the volume of activation for the heme-heme ET was found to be quite distinct from the activation volumes obtained for heme-heme ET in bovine heart Cytochrome c oxidase. Differences in mechanisms/pathways for heme b/heme o(3) and heme a/heme a(3) ET are suggested based on the associated activation volumes and previously obtained Marcus parameters.
authors.affiliation: University of Hawaii at Manoa, Department of Chemistry, 2545 The Mall, Honolulu, HI 96822, USA.
authors.forename: Erin
authors.initials: E
authors.lastname: Ching
authors.forename: Robert
authors.initials: R
authors.lastname: Gennis
authors.forename: Randy
authors.initials: R
authors.lastname: Larsen
mesh_terms: D002248:Carbon Monoxide / Q000378:metabolism; D003573:Cytochrome b Group; D003580:Cytochromes / Q000737:chemistry* / Q000378:metabolism; D004579:Electron Transport; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism; D013053:Spectrophotometry
chemical_list: D003573:Cytochrome b Group; D003580:Cytochromes; D029968:Escherichia coli Proteins; C083850:cytochrome bo3, E coli; D002248:Carbon Monoxide