Nuclear magnetic resonance titration curves of histidine ring protons. A direct assignment of the resonances of the active site histidine residues of ribonuclease.
One of the four titrating histidine ring C-2 proton resonances of bovine pancreatic ribonuclease has been assigned to histidine residue 12. This was accomplished by a direct comparison of the rate of tritium incorporation into position C-2 of histidine 12 of S-peptide (residues 1 to 20) derived from ribonuclease S, with the rates of deuterium exchange of the four histidine C-2 proton resonances of ribonuclease S under the same experimental conditions. The same assignment was obtained by a comparison of the NMR titration curves of ribonuclease S, the noncovalent complex of S-peptide and S-protein (residues 21 to 124) with the results for the recombined complex in which position C-2 of histidine 12 was fully deuterated. The second active site histidine resonance was assigned to histidine residue 119 by consideration of the NMR titration results fro carboxymethylated histidines and 1-carboxymethylhistidine 119 ribonuclease. This assignment is a reversal of that originally reported, and has important implications for the interpretation of NMR titration data of ribonuclease.
D001665:Binding Sites; D003903:Deuterium; D006639:Histidine / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D010446:Peptide Fragments; D011485:Protein Binding; D011487:Protein Conformation; D012260:Ribonucleases
D010446:Peptide Fragments; D006639:Histidine; D003903:Deuterium; D012260:Ribonucleases