title: The role of the imidazolyl nitrogen atoms of histidine-12 in ribonuclease S.
abstract: S-peptide (residues 1--14) analogues in which the active histidine-12 residue is replaced by Npi-methyl-L-histidine, Ntau-methyl-L-histidine and beta-(pyrid-3-yl)-L-alanine were synthesized and tested for their capacity to bind to S-protein and to activate it. The results show that both imidazolyl nitrogen atoms are required for optimal catalytic functioning, Ntau being essential to the catalytic reaction itself, Npi playing a role in keeping the imidazole ring in the correct position.
mesh_terms: D002384:Catalysis; D004789:Enzyme Activation; D006639:Histidine; D009584:Nitrogen; D011485:Protein Binding; D011487:Protein Conformation; D012260:Ribonucleases
chemical_list: D006639:Histidine; D012260:Ribonucleases; D009584:Nitrogen