Inhibition of dextran synthesis by glucoamylase and endodextranase

In a model experiment, glucoamylase was shown to inhibit α-D-glucan synthesis as catalyzed by potato phosphorylase. Both glucoamylase and endodextranase inhibited dextran synthesis with dextransucrases of Leuconostoc mesenteroides. The inhibition could be ascribed to competition between glucoamylase and dextransucrase for the glucosyl groups at the non-reducing end of dextran. The inhibition caused by endodextranase may result from rapid and random hydrolysis of acceptor dextrans. Moreover, significantly low units of glucoamylase, as compared with endodextranase, effectively inhibited dextran synthesis. These results thus present evidence that bio-synthesis of dextran occurs by the addition of glucosyl groups at the non-reducing end of the growing dextran. The measurement of initial velocity suggested that the ping-pong Bi-Bi mechanism proposed for the levansucrase of Bacillus subtilis is also applicable to dextransucrase.