Open AccessInfluence of Leaving-Group Electronic Effect on α-Chymotrypsin: Catalytic Constants of Specific Substrates
Author(s) -
Manfred Philipp,
Ralph M. Pollack,
Myron L. Bender
Publication year - 1973
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.70.2.517
Subject(s) - protonation , chemistry , chymotrypsin , tetrahedral carbonyl addition compound , phenylalanine , michaelis–menten kinetics , leaving group , reaction rate constant , catalysis , hydrolysis , substrate (aquarium) , stereochemistry , tryptophan , computational chemistry , crystallography , kinetics , organic chemistry , enzyme , amino acid , biochemistry , trypsin , enzyme assay , ion , physics , quantum mechanics , nucleophile , oceanography , geology
Rate constants and binding constants for the α-chymotrypsin-catalyzed hydrolysis ofN -acetyltyrosine, tryptophan, and phenylalanine anilides are presented. Bothk cat andK m are independent of electronic effects in the substrate over a range of 9.8 orders of magnitude (as measured by pK of the leaving group). Similarly,K m is independent of charge and orientation about the α-carbon for various substrates and pseudo-substrates. These results are not consistent with the pretransition state protonation hypothesis; instead, they are discussed in terms of a tetrahedral intermediate that is thermodynamically less stable than the Michaelis complex.