Highly multilayered urease decomposes highly concentrated urea

Urease was immobilized at a density of 1.2 g of urease per gram of a matrix via ion-exchange binding of urease to an anion-exchange polymer chain grafted onto a pore surface of a porous hollow-fiber membrane and subsequent cross-linking of urease with transglutaminase. Urea was hydrolyzed during the permeation of a urea solution, the concentration of which ranged from 2 to 8 M, through the pores of the resultant membrane with a thickness of approximately 1 mm. Quantitative hydrolysis of 4 M urea was achieved at a permeation rate lower than 1 mL/h, i.e., a residence time longer than 5.1 min, at ambient temperature. This performance is ascribed to convective transport of urea through the pores rimmed by the urease-immobilized polymer chains at a high density. Urease was denatured in the presence of urea at concentrations higher than 6 M while hydrolyzing urea.