title: A steady-state kinetic analysis of the reaction between arginine esterase E-I from Bitis gabonica venom and synthetic arginine substrates and the influence of pH, temperature and solvent deuterium isotope.
abstract: 1. Using synthetic arginines as substrates, steady-state kinetic studies showed a deviation from Michaelis-Menten kinetics for esterase E-I purified from the venom of Bitis gabonica. Graphical analysis indicated a rate equation of at least a degree of 3:3. 2. pH variation of the kinetic parameters indicated the involvement of groups with pK values of approximately 7 and approximately 9 which had to be in the ionic form for activity. 3. Solvent isotope studies suggested transition states where proton transfer or reorganization was the rate-limiting step of proteolytic catalysis. A single protogenic site was postulated. 4. Temperature effects on the enzymic reaction showed a significant reduction in entropy loss upon formation of the transition state with both esters and extended tail polypeptide-anilides in comparison with the activation entropy for benzoyl-L-arginine p-nitroanilide.
authors.affiliation: Health Chemical Laboratory, Department of National Health and Population Development, Pretoria, Republic of South Africa.
authors.forename: P S
authors.initials: PS
authors.lastname: Gravett
authors.forename: C C
authors.initials: CC
authors.lastname: Viljoen
authors.forename: M M
authors.initials: MM
authors.lastname: Oosthuizen
mesh_terms: D001120:Arginine / Q000138:chemical synthesis / Q000378:metabolism*; D002265:Carboxylic Ester Hydrolases / Q000378:metabolism*; D003903:Deuterium; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D012997:Solvents; D013379:Substrate Specificity; D013696:Temperature; D014757:Viper Venoms / Q000201:enzymology*
chemical_list: D012997:Solvents; D014757:Viper Venoms; D001120:Arginine; D003903:Deuterium; C019724:arginine esterase; D002265:Carboxylic Ester Hydrolases