ACTIVITY OF UREA AMIDOHYDROLASE IMMOBILIZED WITHIN POLY[DI(METHOXYETHOXYETHOXY)PHOSPHAZENE] HYDROGELS

Urea amidohydrolase (urease) was immobilized within poly[di(methoxyeth oxyethoxy)phosphazene] (MEEP) hydrogels. This was accomplished by mixi ng an aqueous solution (pH 7) of the soluble polymer with the enzyme. Films of the conjugate were cast and the solvent removed to yield an M EEP/enzyme composite. The conjugate films were dried in a vacuum and w ere then cross-linked by exposure to 0.2 or 0.5 Mrad of Co-60 gamma-ra diation to give an MEEP network with the enzyme entrapped within its m atrix. The cross-linked films were sectioned into strips and were wash ed with pH 7 buffer to remove enzyme adhering to the surface. The film s were then allowed to swell to form a hydrogel in pH 7 buffer to whic h was added a 1.0 M aqueous urea solution. The increase in pH from the conversion of urea to ammonia was monitored over a 24 h period. The i mmobilized enzyme could be recycled at least five times without signif icant loss of activity. Several control experiments were also performe d by monitoring the pH of buffer solutions that contained hydrogels de void of entrapped urease, and by monitoring the pH of solutions of the free, non-irradiated and free, irradiated urease after the addition o f the urea solution. The polymer-free, irradiated urease lost little t o no activity compared with its nonirradiated counterpart. The MEEP ge l-immobilized enzyme retained approximately 80% of the activity of the non-irradiated, polymer-free urease.