Urease immobilisation on chemically grafted nylon membranes: Part 1: Isothermal characterisation

Urease–HMDA–poly(BMA)–nylon membranes have been prepared by grafting butyl methacrylate (BMA) monomers on nylon sheets. Hexamethylenediamine (HMDA) and glutaraldehyde have been used as spacer and coupling agent, respectively. The catalytic activity of the membrane has been characterised as a function of pH, temperature, and urea concentration. The activity of the free enzyme has also been studied for comparison. The results indicated good enzyme-binding capacity of the pre-treated membrane and a shift of the optimum pH and temperature. These membranes represent an useful system to be used in biotechnological processes occurring under acidic conditions and high temperatures. A three-dimensional (3D) model of the free enzyme has been built by computer simulation with the aim of understanding the enzyme-membrane interaction and the role of β-mercaptoethanol on improving the stability of the catalytic membranes. The use of the catalytic membranes in biosensors or bioreactors operating under non-isothermal conditions has been described as an useful tool to overcome the increased Km value of the immobilised enzyme and the diffusion limitation problems due to the immobilisation procedure.