Armored Urease: Enzyme-Bioconjugated Poly(acrylamide) Hydrogel as a Storage and Sensing Platform

Abstract

Jack bean urease is an important enzyme not only because of its numerous uses in medical and other fields but also because of its historical significance—the first enzyme to be crystallized and also the first nickel metalloenzyme. This enzyme hydrolyzes urea into ammonia and carbon dioxide; however, the stability of this enzyme at ambient temperature is a bottleneck for its applicability. To improve urease stability, it was immobilized on different substrates, particularly on polymeric hydrogels. In this study, the enzyme was coupled covalently with poly(acrylamide) hydrogel with an yield of 18 μmol/cm3. The hydrogel served as the nanoarmor and protected the enzyme against denaturation. The enzyme immobilized on the polymer hydrogel showed no loss in activity for more than 30 days at ambient temperature, whereas free enzyme lost its activity within a couple of hours. The Michaelis–Menten constant (Km) for free and immobilized urease were 0.0256 and 0.2589 mM, respectively, on the first day of the study. The Km of the immobilized enzyme was approximately 10 times higher than that of the free enzyme. The hydrogel technique was also used to prepare light diffracting polymerized colloidal crystal array in which urease enzyme was covalently immobilized. This system was applied for the detection of mercury (Hg2 +) with the lower limit as 1 ppb, which is below the maximum contaminant limit (2 ppb) for mercury ions in water. The experimental details of these studies are presented in this chapter.