[Effect of progressive chemical modification on the activity and thermal stability of soluble and immobilized glucoamylase].

The chemical modification of glucoamylase from Aspergillus niger with acryloylchloride has been studied. It was shown that the first 60--70% of the total amount of available amino groups of the enzyme readily interact with the reagent: the activity and thermal stability of the resulting soluble acryloylglucoamylase are only slightly less than those of the native enzyme. The modification of the remaining 30% of the total amount of amino groups is less intensive and results in a sufficient loss of activity (6 times at 92% modification) and thermal stability (3,5 times at the same degree of modification) by the enzyme. The multipoint immobilization of glucoamylase by mutual covalent attachment of its acryloyl derivative to polyacrylamide gel also causes destabilization of the enzyme. The resulting increase of the number of the enzyme--support binding points leads to a progressive decrease of the enzyme thermal stability as compared to native glucoamylase despite a slight increase in stability (up to 1,5 times) as compared to soluble acryloylglucoamylase. It was shown that destabilization of glucoamylase at 65 degrees due to chemical modification is more pronounced than its negligible stabilization due to the multipoint fixation of glucoamylase on a high polymer support.