Water-insoluble derivatives of enzymes, antigens, and antibodies.

Abstract

Water-insoluble derivatives of proteins with biological activity in which the protein is bound to an insoluble carrier are of practical and theoretical interest. Water-insoluble enzymes have been used as heterogeneous specific catalysts in suspension or in column form. They can be readily removed from the reaction mixture and, if stable, can be employed repeatedly to induce specific chemical changes in relatively large amounts of substrate. Water­ insoluble antigens and antibodies have been used for specifically adsorbing their corresponding antibody or antigen from a mixture of compounds. The adsorbed antibodies were subsequently recovered in pure form by elution. The theoretical interest in biologically active proteins that are bound to well characterized synthetic carriers stems from the tact that such protein de­ rivatives provide simple models for the study of the effect of the micro­ environment on the mode of action of enzymes, or other biologically active proteins, which act in vivo while embedded in membranes or other complex native surroundings. Four principal methods for insolubilization of biologically active proteins have been described: (a) physical adsorption to inert carriers (e.g., glass beads, charcoal or cellulose) or synthetic ion exchange resins; (b) inclusion inside the lattice of a gel, the pores of which are too small to allow the en­ trapped protein to escape; (c) covalent binding of the protein to a suitable water-insoluble carrier; and (d) covalent cross-linking of the protein by a suitable bifunctional reagent. A number of papers have dealt with the preparation by physical adsorp­ tion of insoluble enzyme derivatives (1-12) and antigen derivatives (13-17). However, although in all the cases cited above the insoluble enzyme prep­ arations obtained were shown to be enzymatically active, only in the work of Nelson and his co-workers (1, 2), was it shown that there was no detectable desorption of enzyme under the conditions of assay. In general, it may be said that even if under a given set of conditions no active protein is eluted from an adsorbent, changing the ionic strength, pH or temperature, or addi­ tion of substrate (particularly when the substrate is a charged macromole­ cule) may bring about partial or total desorption. It may, therefore, be