title: Kinetic compensation and the role of cations in pectinesterase catalysis.
abstract: The catalytic rate constant of thermostable pectinesterase (TS-PE) from Marsh grapefruit pulp was determined at pH 7 at temperatures between 25 and 60 degrees C. TS-PE activity was measured at NaCl concentrations of 0.05, 0.10, 0.15, and 0.20 M and at CaCl(2) concentrations of 0.005, 0.010, 0.015, and 0.020 M. For sodium- and calcium-added conditions, the kinetic functions of this reaction agreed with kinetic compensation relations. The isokinetic temperatures for sodium- and calcium-added conditions were 327.8 and 312.4 K, respectively. Different isokinetic temperatures and compensation parameters suggest that sodium and calcium uniquely affect TS-PE catalysis. This is the first demonstration of kinetic compensation in an enzyme-catalyzed reaction.
authors.affiliation: Department of Food Science and Technology, University of Georgia, Athens 30602, USA.
authors.forename: D
authors.initials: D
authors.lastname: Sun
authors.forename: L
authors.initials: L
authors.lastname: Wicker
mesh_terms: D002122:Calcium Chloride / Q000494:pharmacology; D002265:Carboxylic Ester Hydrolases / Q000378:metabolism*; D002384:Catalysis; D002412:Cations / Q000494:pharmacology; D002957:Citrus / Q000201:enzymology*; D004795:Enzyme Stability; D007700:Kinetics; D012965:Sodium Chloride / Q000494:pharmacology; D013816:Thermodynamics
chemical_list: D002412:Cations; D012965:Sodium Chloride; D002265:Carboxylic Ester Hydrolases; C022323:pectinesterase; D002122:Calcium Chloride