Enzyme Immobilization in Biotechnology
Cynthia Spahn and Shelley D. Minteer*
Department of Chemistry, Saint Louis University, 3501 Laclede Ave., St. Louis, MO 63103, USA
Received: July 30, 2008; Accepted: August 27, 2008; Revised: September 2, 2008
Abstract: Enzymes are proteins that catalyze chemical reactions. Unlike moretraditional organic and inorganic catalysts, enzymes are large and fragile molecules, so over the years, scientists and engineers have found it more difficult to immobilize enzyme catalysts on easily separateable supports for use and re-use in a variety of technologies. Over the last decade, enzyme immobilization has become more important in industry, medicine, and biotechnology. This review will detailrecent patents for techniques for enzyme immobilization, along with patents for chemical and biotechnological processes that can employ immobilized enzymes, which allow for the re-use of the enzymatic catalysts. These techniques include methods varying from physical adsorption and covalent attachment to entrapment in polymers and sol-gels. These techniques have shown value in the development ofbiosensors, bioprocessing for the chemical industry and the pharmaceutical industry, and bioremediation.
Keywords: Enzyme immobilization, entrapment, physical adsorption, crosslinking, covalent binding, biosensors, biotechnology, biocatalysis. INTRODUCTION Many technologies have been affected or could be affected in the near future by the immobilization of enzymes. The ability of enzymes to catalyzereactions has made them indispensable to science for decades . The immobilization of enzymes has proven particularly valuable, because it has allowed enzymes to be easily reused multiple times for the same reaction with longer half-lives and less degradation and has provided a straightforward method of controlling reaction rate as well as reaction start and stop time. It has also helped toprevent the contamination of the substrate with enzyme/protein or other compounds, which decreases purification costs. These benefits of immobilized enzymes have made them highly applicable to a range of evolving biotechnologies . There are a variety of methods used to immobilize enzymes. Three of the most common being adsorption, entrapment, and cross-linking or covalently binding to a support,as is shown in Fig. (1). Regardless of the method of immobilization, the material in which the enzyme is immobilized in must be insoluble in the solvent, which is frequently water. The adsorption method involves the enzyme being physically adsorbed onto the backbone or support material, often a polymer matrix (i.e. polymer beads or membranes). This technique is relatively simple, because ittypically either involves bathing the support in a solution of the enzyme and incubating to allow time for the physical adsorption to the surface to occur or allowing a solution of the enzyme to dry on the electrode surfaces and then rinsing away enzyme that is not adsorbed [3,4]. Unfortunately this method is troublesome, because it allows leaching of the enzyme while reacting, thereby, contaminating thesubstrate [5, 6]. Physical adsorption can also denature the enzyme depending on the surface chemistry of the support material.
*Address correspondence to this author at the Department of Chemistry, Saint Louis University, 3501 Laclede Ave., St. Louis, MO 63103, USA; Tel: 314-977-3624; E-mail: firstname.lastname@example.org
The entrapment method involves entrapping enzyme in either the lattice structure ofa material or in polymer membranes [7-9]. This usually minimizes enzyme leaching and improves stabilization, but frequently results in transport limitations of substrate/analyte to the enzyme active site. However, this technique allows for the ability to tailor the encapsulating material to provide the optimal microenvironment for the enzyme (i.e. matching the physico-chemical environment of the...