title: Catalytic activity of  -chymotrypsin in which histidine-57 has been methylated.
abstract: The properties of a derivative of alpha-chymotrypsin in which histidine-57 has been methylated have been examined. Although the modified enzyme binds substrate with the same affinity as does native alpha-chymotrypsin, acylation and deacylation occur at much decreased rates. As for native alpha-chymotrypsin, a basic group of pK(a) approx. 7 is involved in both acylation and deacylation. The significance of these results is considered in relation to the normal function of histidine-57.
mesh_terms: D000166:Acridines; D000215:Acylation; D000577:Amides; D002384:Catalysis; D002845:Chromatography; D002918:Chymotrypsin; D004952:Esters; D006639:Histidine; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D008745:Methylation; D009596:Nitrophenols; D012694:Serine
chemical_list: D000166:Acridines; D000577:Amides; D004952:Esters; D009596:Nitrophenols; D012694:Serine; D006639:Histidine; D002918:Chymotrypsin