Sunday, April 29, 2007

Immobilization of fungal beta-glucosidase on silica gel and kaolin carriers

Hakob K. Karagulyan1, Vardan K. Gasparyan1, and Stephen R. Decker2. (1) Institute of Biotechnology, 14 Gyurjyan str., Yerevan, Armenia, (2) Chemical and Biosciences Center, National Renewable Energy Laboratory, 1617 Cole Blvd, Golden, CO 80401

Beta-glucosidase is a key enzyme in the hydrolysis of cellulose for producing feedstock glucose for various industrial processes.  Reuse of enzyme through immobilization can significantly improve the economic characteristics of the process.  Immobilization of the fungal b-glucosidase by covalent binding and physical adsorption on silica gel and kaolin was conducted for consequent application of these procedures in large scale industrial processes.  Different immobilization parameters (incubation time, ionic strength, pH, enzyme/support ratio, glutaric aldehyde concentration, etc.) were evaluated for their effect on the thermal stability of the immobilized enzyme.  It was shown that the immobilized enzyme activity is stable at 50o C over 8 days.  It has also been shown that in the case of immobilization on kaolin, approximately 95% of the initial enzyme was immobilized onto support and loss of activity was not observed.  However, covalent binding of the enzyme to silica gel brings significant loss of enzyme activity and only 35% of activity was preserved.  In the case of physical adsorption on kaolin, gradual desorption of enzyme takes place.  In order to prevent this process, we have carried out chemical modification of the protein.  As a result, after repeated washings, enzyme desorption from kaolin has been reduced from 75% to 20-25% loss.