Improved stability of proteins immobilized in microparticles prepared by a modified emulsion polymerization technique

Proteins can be immobilized in spherical microparticles of polyacrylamide gel (having a diameter of about 1 microgram) by an emulsion--polymerization technique. Higher cross-linked gels have a structure consisting of relatively large pores. This structure is advantageous when dealing with biologically active proteins acting on molecules dissolved in the surrounding medium. A rapid equilibrium is established between the interior of the particles and the medium, and rate-limiting diffusion is not observed. A suspension of carbonic anhydrase immobilized in microparticles will thus have kinetic properties very much like the free enzyme. In addition to the entrapment of the protein molecules in the three-dimensional network formed by the polyacrylamide threads, protein molecules are also fixed in the cross-linked threads of polyacrylamide. This fixation is probably responsible for the improved stability of the protein molecules against heat denaturation. Not even autoclaving at 110 degrees for 30 min denatured the immobilized enzyme completely (more than 25% of the enzyme activity was left). The higher resistance of molecules in microparticles against proteolytic degradation also is documented.