title: Evidence for heme-heme excitonic coupling in the Soret circular dichroism of hemoglobin.
abstract: In order to study interdimer heme-heme electronic interactions in human hemoglobin, the Soret circular dichroism spectrum of the carboxy adduct is measured as a function of protein concentration, the spectrum at the highest concentration representing primarily that of alpha2beta2 tetramers (93%) and the lowest concentration representing primarily alphabeta dimers (68%). The tetramer-dimer difference spectrum, obtained using singular value decomposition and linear least squares fitting from a matrix of CD spectra measured at ten concentrations, is roughly conservative, with a larger negative lobe at shorter wavelengths and a peak-to-trough magnitude that is 18% of the tetramer's maximum Soret CD magnitude. It is tentatively assigned to heme-heme excitonic interactions on the basis of theoretical predictions by R. W. Woody [(1985) in Optical Properties and Structure of Tetrapyrroles (Blauer, G., and Sund, H., Eds.), pp. 239-256, Walter de Gruyter, New York].
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Santa Cruz 95064, USA. goldbeck@chemistry.ucsc.edu
authors.forename: R A
authors.initials: RA
authors.lastname: Goldbeck
authors.forename: L
authors.initials: L
authors.lastname: Sagle
authors.forename: D B
authors.initials: DB
authors.lastname: Kim-Shapiro
authors.forename: V
authors.initials: V
authors.lastname: Flores
authors.forename: D S
authors.initials: DS
authors.lastname: Kliger
mesh_terms: D002263:Carboxyhemoglobin / Q000737:chemistry; D002942:Circular Dichroism; D019281:Dimerization; D006418:Heme / Q000737:chemistry*; D006454:Hemoglobins / Q000737:chemistry*; D006801:Humans; D046911:Macromolecular Substances; D011487:Protein Conformation; D013053:Spectrophotometry
chemical_list: D006454:Hemoglobins; D046911:Macromolecular Substances; D006418:Heme; D002263:Carboxyhemoglobin