Preparation and Property of Urease Immobilization with Cationic Poly(4-vinylpyridine) Functionalized Colloidal Particles

Urease (urea amidohydrolase, EC 3.5.1.5), widely distributed in nature, catalyzes the hydrolysis of urea to ammonia and carbon dioxide at a rate 1014 times faster than the uncatalyzed reaction.1–3 Among enzymes, urease is most extensively studied for immobilization due to the possible exploitation in practical applications, such as quantitative determination of blood urea in clinical examination and detection of heavy metal ions in environment.4,5 It has been found that the immobilization of the enzyme enables the repeated use of the enzyme and thereby reduces the operating costs, as well as enhances stability and facilitates easy separation.6 In the past decade, many immobilization approaches have been developed to immobilize the enzyme and a variety of matrixes have been used for urease immobilization.7–16 Among them, polymeric microspheres have attracted much attention because they can be modified easily by functional groups for immobilization. For example, Elcin et al. immobilized urease within polyanionic carboxymethylcellulose/ alginate microspheres coated with a cationic chitosan;17 Kayastha et al. reported ureases from jack beans (Urs-JB) and pigeonpea (Urs-PP) had been immobilized onto poly(styrene-co-acrolein) microspheres.18 However, for the various matrixes used as immobilization supports, the low loading capacity always resulted in low efficacy of the immobilized enzyme and limited their practical application.19 Therefore, there is still constant exploration for new immobilization matrix until now. The low loading capacity is always associated with the few sites for enzyme immobilization and low specific surface area. In our previous work, we developed a new microsphere support consisting of cationic poly(4-vinylpyridine) hairy colloidal particles for protein adsorption (such as bovine serum albumin). The capacity of protein adsorption could reach a high capacity of about 900 mg g–1, because the chain length of charged hairy could be changed by the controlled synthesis, and there is a high specific area due to the nanosize (~50 nm).20 Furthermore, the positive charges of the microsphere support remained at constant value in the entire pH range, and so it could be used to adsorb the protein with different isoelectric point (pI). We expect that this kind of nanoparticles as supports can provide more sites and high specific surface area for immobilizing enzymes, thereby leading to high loading capacity for enzymes and high catalytic efficiency. Preparation and Property of Urease Immobilization with Cationic Poly(4-vinylpyridine) Functionalized Colloidal Particles