title: A steady state analysis of pH and temperature effects on the action of an arginine esterase from the venom of the gabon adder, Bitis gabonica, on synthetic arginine substrate.
abstract: The influence of pH and temperature on the kinetic properties of esterase E-II from Bitis gabonica venom has been studied. The pH profiles for the hydrolysis of N alpha-benzoyl-L-arginine ethyl ester showed that a group with pK approximately 7 must be ionized for activity. Measurement of N alpha-benzyl-L-arginine-p-nitroanilide hydrolysis reveals that the pK of the active site is significantly lowered (i.e. to approximately 6.3) in the enzyme-substrate complex. The temperature effect on the pK suggests the presence of a carboxylate in the active site of the enzyme. This suggestion is corroborated by the influence of organic solvent perturbations of the pK indicating a catalytic group of the neutral acid type. Values for the thermodynamic parameters associated with activation are reported. The transition state for ester degradation is at lower delta G and delta H levels than that for amide degradation. delta H and delta S for ester hydrolysis were noted to compensate each other with a compensation temperature Tc = 339K. Compensation can probably be related to weak bonding effects.
mesh_terms: D000818:Animals; D001120:Arginine; D002265:Carboxylic Ester Hydrolases / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D013379:Substrate Specificity; D013696:Temperature; D013816:Thermodynamics; D014757:Viper Venoms / Q000378:metabolism*
chemical_list: D014757:Viper Venoms; D001120:Arginine; C019724:arginine esterase; D002265:Carboxylic Ester Hydrolases