title: Assignments of 15N and 1H NMR resonances and a neutral pH ionization in Rhodospirillum rubrum cytochrome c2.
abstract: The phi NH proton and 15N resonances of the ligand histidine of Rhodospirillum rubrum fericytochrome c2 are found at 14.7 and 184 ppm, respectively, contradicting the proposal that this proton is absent in the R. rubrum ferricytochrome. Substitution of the deuterium atom for this proton causes small upfield shifts of the phi nitrogen in both oxidation states, indicating that the phi NH-peptide carboxyl hydrogen bond is not substantially weakened by the substitution. The proton and 15N resonances of the indolic NH group of the invariant tryptophan-62 and numerous proton resonances of the heme and extraheme ligands in the spectrum of the ferricytochrome are also assigned. An ionization in the ferrocytochrome occurring at neutral pH is assigned to the single nonligand histidine. This attribution is supported by the direct measurement of the ionization by NOE difference spectroscopy and by comparative structural arguments involving closely related cytochromes and chemically modified cytochromes.
authors.affiliation: Department of Food Science and Technology, University of California, Davis 95616.
authors.forename: L P
authors.initials: LP
authors.lastname: Yu
authors.forename: G M
authors.initials: GM
authors.lastname: Smith
mesh_terms: D000643:Ammonium Chloride; D003574:Cytochrome c Group / Q000378:metabolism*; D045362:Cytochromes c2; D006859:Hydrogen; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D009587:Nitrogen Isotopes; D011487:Protein Conformation; D012247:Rhodospirillum rubrum / Q000378:metabolism*
chemical_list: D003574:Cytochrome c Group; D009587:Nitrogen Isotopes; D000643:Ammonium Chloride; D006859:Hydrogen; D045362:Cytochromes c2