Effectors Differently Modulating the Dextransucrase Activity of Leuconostoc mesenteroides

Effects of various compounds on the dextransucrase (EC 2.4.1.5) from Leuconostoc mesenteroides was evaluated based on the two catalytic activities of enzyme, that is the hydrolase activity for the substrate, sucrose, and the transferase activity of a d-glucosyl group to an acceptor molecule. The effectors were grouped into six categories by their activation or inhibition of the sucrase and transferase activities of dextransucrase. Type I-A inhibited both activities, type I-B inhibited the sucrase activity, and type I-C inhibited the transferase activity. Type A-A activated both the hydrolase and transferase, and type A-B activated only the transferase. Antagonistic modulation (type IA-A), was shown by methyl α-d-glucoside and glycerol, which activated the sucrase and inhibited the transferase. A double reciprocal plot for dextran gave a biphasic pattern which led to Ki values for each limb. Based on the biphasic kinetics and the action of antagonistic effectors, the regulation of dextran synthesis was discussed.