title: The second nucleophile molecule binds to the acyl-enzyme-nucleophile complex in alpha-chymotrypsin catalysis. Kinetic evidence for the interaction.
abstract: alpha-Chymotrypsin-catalyzed acyl transfer was studied using three acyl-group donors (Mal-L-Ala-L-Ala-L-PheOMe, Bz-L-TyrOEt and Ac-L-TrpOEt; Mal, maleyl; Bz, benzoyl; OMe, methyl ester; OEt, ethyl ester) and a series of amino-acid amides. Most of the reactions studied can be described by the simplest kinetic model without the nucleophile binding to the acyl-enzyme. The alpha-chymotrypsin-catalyzed transfer of the Mal-L-Ala-L-Ala-L-Phe group to the amides of L-Phe and L-Tyr showed a linear dependence of the partition constant, p, on the nucleophile concentration which can be interpreted by the hydrolysis of the acyl-enzyme-nucleophile complex. The alpha-chymotrypsin-catalyzed transfer of the Bz-L-Tyr and Ac-L-Trp groups to several amino-acid amides showed unusual behavior which can be interpreted by the kinetic model involving formation of a complex of the acyl-enzyme with two nucleophile molecules. These observations can explain the conflicting conclusions concerning the kinetics of alpha-chymotrypsin-catalyzed acyl transfer evident in previous studies.
authors.affiliation: Department of Biotechnology, University of Lund, Sweden.
authors.forename: M Y
authors.initials: MY
authors.lastname: Gololobov
authors.forename: V M
authors.initials: VM
authors.lastname: Stepanov
authors.forename: T L
authors.initials: TL
authors.lastname: Voyushina
authors.forename: P
authors.initials: P
authors.lastname: Adlercreutz
mesh_terms: D000215:Acylation; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002384:Catalysis; D002417:Cattle; D002918:Chymotrypsin / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D010179:Pancreas / Q000201:enzymology; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism
chemical_list: D010446:Peptide Fragments; D002918:Chymotrypsin