title: The exchange of histidine C-2 protons in superoxide dismutases. A novel method for assigning histidine-metal ligands in proteins.
abstract: The rates of exchange of the C-2 protons of histidine residues in copper-zinc superoxide dismutase are substantially decreased by metal ion binding. This observation was used to distinguish between ligand and non ligand histidine residues in bovine and yeast copper-zinc superoxide dismutases; the effect was shown to depend only on metal ion co-ordination and not as a consequence of concomitant changes in protein structure. Selective deuteration of the zinc-only proteins at pH (uncorrected pH-meter reading) 8.2 and 50 degrees C resulted in the distinction between copper and zinc ligand resonances in the 1H n.m.r. spectrum of the enzymes. This method is proposed as a generally applicable technique for identifying histidine residues as ligands in metalloproteins.
mesh_terms: D000818:Animals; D002417:Cattle; D055598:Chemical Phenomena; D002621:Chemistry; D003300:Copper; D003903:Deuterium; D006639:Histidine; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008722:Methods; D011522:Protons; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D013482:Superoxide Dismutase / Q000097:blood; D015032:Zinc
chemical_list: D008024:Ligands; D011522:Protons; D006639:Histidine; D003300:Copper; D003903:Deuterium; D013482:Superoxide Dismutase; D015032:Zinc