title: Enzymic properties of nitrated alpha-chymotrypsin and delta-chymotrypsin.
abstract: Chymotrypsinogen A and alpha-chymotrypsin are both nitrated at tyrosines 146 and 171 by reaction with tetranitromethane. This substitution was essentially without influence on the overall rate constant for hydrolyses of N-acetyl-L-tryptophan methyl ester and N-acetyl-L-tyrosine ethyl ester catalyzed by alpha-chymotrypsin and delta-chymotrypsin, prepared by fast tryptic activation of nitrated chymotrypsinogen. With both ester substrates Km was doubled for nitrated alpha-chymotrypsin. Nitrated alpha-chymotrypsin, nitrated delta-chymotrypsin and delta-chymotrypsin could all bind N-acetyl-L-tryptophan methyl ester at alkaline pH, in contrast to alpha-chymotrypsin. The dissociation constant, Kd, of the complex of alpha-chymotrypsin and basic pancreatic trypsin inhibitor was lowered ten-fold relative to the constant obtained with unmodified alpha-chymotrypsin. The nitrated delta-chymotrypsin and delta-chymotrypsin showed identical Kd values. The nitrated alpha-chymotrypsin is inactivated faster at pH 8.0 and 8.5 than alpha-chymotrypsin and apparently by a different mechanism.
mesh_terms: D002918:Chymotrypsin / Q000378:metabolism*; D002919:Chymotrypsinogen / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009566:Nitrates; D014361:Trypsin Inhibitors / Q000494:pharmacology; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism
chemical_list: D009566:Nitrates; D014361:Trypsin Inhibitors; D014443:Tyrosine; D002919:Chymotrypsinogen; D002918:Chymotrypsin