title: Estimation of the orientation of heme in cytochrome C immobilized on a carboxylate-terminated alkanethiol monolayer on a au electrode by the use of electroreflectance spectroscopy with polarized light incidence.
abstract: Electroreflectance (ER) spectroscopy was used for the estimation of the orientation of heme in a horse heart cytochrome c molecule immobilized on a self-assembled monolayer of 11-mercaptoundecanoic acid on both polycrystalline gold (Au) and single crystalline Au(111) electrodes. The intensity ratio of the ER signal of p-polarized incident light against s-polarized incident light as a function of the incident angle of the light was analyzed in two ways: a doubly degenerate transition for the Soret absorption band of the heme was assumed in one, and the anisotropy of the two orthogonal transitions was taken into account in the other. The doubly degenerate model failed in the expression of the experimental data, pointing to the existence of the anisotropy. Two orthogonal in-plane linear electric dipoles with different magnitudes were assumed to be responsible for the Soret band absorption in a new analysis procedure. This enabled us to fit the experimental data closely to the simulated data. The result revealed that the heme plane is near-vertical to the electrode surface. The need of clarification of the anisotropic heme transition was invoked.
authors.affiliation: Department of Applied Chemistry, Nagasaki University, Bunkyo 1-14, Nagasaki 852-8521, Japan. sagara@nagasaki-u.ac.jp
authors.forename: Takamasa
authors.initials: T
authors.lastname: Sagara
authors.forename: Yuu
authors.initials: Y
authors.lastname: Kubo
authors.forename: Keizo
authors.initials: K
authors.lastname: Hiraishi
mesh_terms: D000473:Alkanes / Q000737:chemistry; D000818:Animals; D016880:Anisotropy; D002264:Carboxylic Acids / Q000737:chemistry; D045304:Cytochromes c / Q000737:chemistry*; D004563:Electrochemistry; D004566:Electrodes; D004800:Enzymes, Immobilized; D006046:Gold / Q000737:chemistry*; D006418:Heme / Q000737:chemistry*; D006736:Horses; D008027:Light; D008954:Models, Biological; D009206:Myocardium / Q000201:enzymology; D009904:Optical Rotation; D013057:Spectrum Analysis / Q000379:methods; D013438:Sulfhydryl Compounds / Q000737:chemistry; D013499:Surface Properties
chemical_list: D000473:Alkanes; D002264:Carboxylic Acids; D004800:Enzymes, Immobilized; D013438:Sulfhydryl Compounds; D006418:Heme; D006046:Gold; D045304:Cytochromes c