title: Surface of cytochrome c: infrared spectroscopy of carboxyl groups.
abstract: The carboxylate groups of organic acids give strong absorption in the infrared between approximately 1550 and 1650 cm-1. For acetate and chloroacetate derivatives, the infrared (IR) frequency of the carboxylate antisymmetric stretching mode (v(a)OCO) is related to the square root of the pK of the acid, with a shift of approximately 20 cm-1 to higher frequency for a pK drop in the range 5-3. It follows that v(a)OCO may respond to conditions on the protein surface. In this paper, the IR amide I' and carboxylate absorptions of cytochrome c from horse, yeast, and tuna are compared with model compounds such as Val-Glu and microperoxidase-11, the 11 amino acid fragment of horse cytochrome c containing the covalently bound heme. For microperoxidase-11, the contribution from all four carboxylates can be accounted for and the 1567 cm-1 absorption is assigned to the heme propionates. For the proteins, the carboxylate absorption band is inhomogeneous, i.e., there is a distribution of frequencies. Both the amide I' and carboxylate bands are sensitive to protein conformation as shown by their different pH, salt, and redox dependence.
authors.affiliation: Johnson Research Foundation, Department of Biochemistry and Biophysics, School of Medicine, University of Pennsylvania, Philadelphia 19104, USA.
authors.forename: W W
authors.initials: WW
authors.lastname: Wright
authors.forename: M
authors.initials: M
authors.lastname: Laberge
authors.forename: J M
authors.initials: JM
authors.lastname: Vanderkooi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002264:Carboxylic Acids / Q000737:chemistry*; D003574:Cytochrome c Group / Q000737:chemistry*; D017666:Deuterium Oxide; D004151:Dipeptides / Q000737:chemistry; D006736:Horses; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D010544:Peroxidases / Q000737:chemistry; D013045:Species Specificity; D013055:Spectrophotometry, Infrared; D017186:Titrimetry; D014413:Tuna; D014867:Water; D015003:Yeasts
chemical_list: D002264:Carboxylic Acids; D003574:Cytochrome c Group; D004151:Dipeptides; D010446:Peptide Fragments; D014867:Water; D010544:Peroxidases; C021799:microperoxidase; D017666:Deuterium Oxide