UREASE IMMOBILIZED ON AN AMINATED POLYSULFONE MEMBRANE - INHIBITION BY BORIC-ACID

An enzymatic membrane for application in the processes of decompositio n and removal of urea from aqueous solutions was prepared: jack bean u rease was immobilized on an aminated polysulphone membrane by adsorpti on. The inhibition of the system by boric acid was studied using proce dures based on the MICHAELIS-MENTEN integrated equation (non-linear re gression, and the linear transformations of WALKER and SCHMIDT, JENNIN GS and NIEMANN, and BOOMAN and NIEMANN). The reaction was carried out in a 100 mM phosphate buffer of pH 7.0, containing 2 mM EDTA, obtained by neutralization of orthophosphoric acid with NaOH, at an initial ur ea concentration of 10 mM, and a temperature of 25 degrees C. The reac tion was initiated by the addition of the enzyme to the urea solution, and was monitored by removing samples of the reaction mixture for NH3 determinations by the phenol-hypochlorite method until the urea was e xhausted. The results were compared with those obtained earlier under the same reaction conditions for free urease and urease covalently imm obilized on chitosan. The inhibition was found to be competitive, simi lar to that of the free enzyme and urease immobilized on chitosan, wit h inhibition constants K-i equal to 0.36, 0.19 and 0.60 mM. The result s show that adsorption of the enzyme on a polysulphone membrane change d the enzyme to a lesser degree than covalent immobilization of the en zyme on a chitosan membrane.