Stabilization and Activation of Enzymes by Adsorptive Immobilization with Water-Soluble Polymers and Its Application to Enzyme Membrane Reactor

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1. Stabilization of enzymes and accelerating effect of water-soluble polymers on enzymic reaction(1) By addition of water-soluble cationic polymers such as polyethyleneimine(PEI) and DEAE-dextran, thermal stability of glucose dehydrogenase (GDH) was remarkably increased. It was deduced that adsorption of polymers to GDH prevents unfolding of GDH by multi-point binding.(2) The rate of GDH-catalyzed reaction was enhanced by addition of PEI at low coenzyme(NAD()^+) concentration. The results of kinetic study suggested that the accelerating effect is due to PEI-mediated enrichment of coenzyme NAD(P)^+ near GDH interacting with PEI.(3) In the reduction of phenylpyruvic acid(PhP) by lactate degydrogenase(LDH)/GDH conjugate system, addition of PEI was very effective for increasing reaction rate.(4) The apparent equilibrium constant of alcohol dehydrogenase(ADH)-catalyzed reaction was increased by addition of PEI, resulting in improvement of the conversion of PhP in LDH/ADH-catalyzed reaction.2. Effect of water-soluble polymers on performance of enzyme membrane reactorIn the continuous reduction of PhP by the LDH/GDH conjugate enzyme system using a continuoustype hollow fiber enzyme reactor, addition of PEI was effective for increasing the conversion of PhP.3. Preparation of microporous charged membrane by plasma-graft polymerization for membrane enzyme reactor.Microporpus charged membranes were prepared by grafting acrylic acid to microporous polyethylene membranes, and the effect of preparation condition of the membrane properties was studied. Membranes with high charge density were successfully prepared.