Preparation, properties and uses of polymer‐enzyme conjugates

Abstract

AbstractEnzymes can be immobilized by gel entrapment, by microencapsulation, by physical or ionic adsorption, by covalent binding to inorganic or organic carriers, or by whole cell immobilization. Of particular interest is the large number of chemical reactions developed for the covalent binding of enzymes via their nonessential functional groups to inorganic carriers such as glass, ceramics and iron, to natural polymers such as cellulose and Sepharose, and to synthetic polymers such as nylon, polyacrylamide, and other vinyl polymers and copolymers possessing reactive chemical groups. The stability of certain enzymes is markedly increased on their immobilization. It was thus possible to transform the biologically active polymer derivatives into active enzyme beads, enzyme capsules, enzyme columns and enzyme membranes and these enabled the construction of enzyme reactors such as the batch‐stirred tank reactors, the continuous packed bed reactors, and fluidized bed reactors. So far mainly immobilized hydralases and isomerases are being used in industry on a large scale. It seems likely, however, that once adequate techniques become available for cofactor recycling, the use of immobilized enzymes will be extended to other organic reactions, particularly those involving stereospecific synthesis of simple or complex organic molecules. Among the industrial processes in which immobilized enzymes are being used, it is worth mentioning the industrial‐scale continuous production of fructose enriched syrup from glucose by immobilized glucose‐isomerase, the batch process for the production of 6‐aminopenicillanic acid (6‐APA) from penicillin G with the aid of immobilized penicillin amidase; the production of aspartame from aspartic acid and phenylalanine by immobilized thermoase; the large scale production of optically active amino acids with immobilized amino acid acylase; and the large scale production and application of immobilized lactase for the hydrolysis of lactose. The recently developed process for acrylamide production using immobilized nitrilase containing microbial cells should also be referred to. The successful use of an NAD‐polyethylene glycol conjugate (NAD‐PEG) as a nondialyzable water‐soluble coenzyme derivative in the enzymic synthesis of leucine from α‐ketoisocaproic acid and ammonia, in a membrane‐enclosed reactor containing L‐leucine dehydrogenase, NAD‐PEG, formate and formate dehydrogenase, illustrates the new possibilities opened up by making use of cofactor‐polymer conjugates. The use of enzyme‐polymer conjugates in analytical and clinical is also illustrated.