Cross Binding Method
The enzyme can be immobilized by cross-linking to a multifunctional reagent without involving a solid support. Alternatively, a chemical bridge (analogous to the spacer arm in affinity chromatography) of some other molecule can be established between the enzyme and a chemical support. The reagent or the bridge chemical, reacts with the enzyme and forms a linkage. Some of the commonly used reagents for cross-linking enzymes. There types of basic approaches have been used in immobilizing enzymes by cross-linking. (i) Cross-linking of enzyme with glutaraldehyde to form an insoluble aggregate; e.g. papain. (ii) Adsorption of enzyme onto a surface followed by cross-linking; for instance, cross-linking trypsin adsorbed to the surface of colloidal silica particles. (iii) Impregnation of porous material with the enzyme followed by cross-linking of the enzyme in the pores; for instance, papain in collodion membrane.