Hydrolysis catalyzed with a resin containing histidine groups

Abstract

A histidine-containing polymer was synthesized in which the amino group of the histidine was attached chemically via an azide coupling method to the carboxylic acid of Amberlite IRC-50. The resultant polymer was applied as a catalyst for hydrolysis of p-nitrophenyl acetate (PNPA). PNPA in aqueous solution was hydrolyzed at 25°C with a phosphate buffer (pH 7.8). The observed kinetics obey those of Michaelis-Menten. The reaction rates at various temperatures were measured. The activation parameters, pre-exponential factor ( A) and activation energy ( E a), were 6.64 × 10 −4 min −1 and 37.5 kJ mol −1 respectively. At a pH of the medium greater than 7.8, the reaction rate remained almost constant ( k obs = 0.024 min −1) and seemed to be controlled by the rate of diffusion of PNPA from the bulk solution into the catalytically active site at the resin channel surface. For catalysed hydrolysis, the effect of ionic strength in solution demonstrated that bifunctional cooperation between adjacent histidine groups existed through the nucleophilicity of nitrogen. The effects of metal ions and aspartic acid or serine on hydrolysis were also investigated.