CONDENSATION OF GLUCOSE BY THE REVERSED HYDROLYSIS REACTION OF GLUCOAMYLASE .2. EFFECT OF INHIBITION OF GLUCOSE DERIVATIVES AND PH

Glucose has two anomer types (alpha- and beta-D-glucose). The inhibiti ng effect of the methyl-alpha- and methyl-beta-D-glucoside, and 6-deox y-D-glucose on synthesis of isomaltose as main product in the reaction mixture were investigated. It was found that the Ki values for methyl -alpha-D-glucoside and methyl-beta-D-glucoside were 75 and 1.0 mol l(- 1), respectively, which means that the role of the beta-configuration of glucose for synthesis was confirmed and supported well. Thus, the K i value for 6-deoxy-D-glucose was 0.41 mol l(-1), which indicates a mu ch stronger inhibition compared to the methyl-alpha- and methyl-beta-D -glucoside. The effect of pH on the synthesis of isomaltose was also s tudied at 55 degrees C over the range of pH 3.0 to 7.0 and 54% (w/v) g lucose solution. The optimum pr I for the synthesis of isomaltose by t he reversed hydrolysis reaction of glucoamylase from A. niger was appr oximately 4.8, which was in accordance with the values reported in the literature for the hydrolysis of starch (pH 4.5), maltose and isomalt ose (pH 5.0). It means that both of the function groups of the glucoam ylase take part in synthesis and hydrolysis, too.