title: Hydrogen-tritium exchange titration of the histidine residues in bovine heart cytochrome c and analysis of their microenvironment.
abstract: Microenvironments of the three histidine residues located at the positions 18, 26, and 33 from the amino terminus in bovine heart cytochrome c were analysed in solution by the hydrogen-tritium exchange titration method, which has been developed in this laboratory. Histidine-18, which is liganded to the heme iron, and histidine-26 did not incorporate tritium in native state, indicating that the two are located in solvent inaccessible hydrophobic regions. Histidine-33 was labeled with tritium to an appreciable extent and seemed to be partially buried in the molecule. The pKa value estimated for histidine-33 was 6.1 at 37 degrees by the tritium exchange titration, suggesting that the residue interacts very weakly with a neighboring cationic group. These results seem to be compatible with the tertiary structure of the protein deduced from the X-ray crystallographic analysis.
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002417:Cattle; D055598:Chemical Phenomena; D002621:Chemistry; D003574:Cytochrome c Group; D006639:Histidine; D006859:Hydrogen; D006863:Hydrogen-Ion Concentration; D009206:Myocardium / Q000201:enzymology; D014316:Tritium
chemical_list: D000596:Amino Acids; D003574:Cytochrome c Group; D014316:Tritium; D006639:Histidine; D006859:Hydrogen