Acceptor reactions and mechanism of Leuconostoc mesenteroides B-512FM dextransucrase

Although Hanes-Woolf plot showed that methyl [alpha]-D-glucopyranoside was an apparent competitive inhibitor for dextransucrase, a Michaelis-Menten plot using methyl [alpha]-D-glucopyranoside in the presence of high concentration of sucrose showed that it was not a real competitive inhibitor. We have also found that methyl 6-deoxy-[alpha]-D-glucopyranoside and methyl 6-deoxy-6-fluoro-[alpha]-D-glucopyranoside were weak inhibitors, whereas the corresponding sucrose analogues 6-deoxysucrose and 6-deoxy-6-fluorosucrose are very potent inhibitors for dextransucrase. From these findings, it is concluded that the acceptor, methyl [alpha]-D-glucopyranoside, does not compete with sucrose for the sucrose binding-sites and it binds at a separate acceptor binding-site;A model, based on the known mechanisms of dextran synthesis and acceptor reactions, is proposed to explain the inhibition of dextran synthesis, and the increase in the acceptor products at high sucrose concentrations. According to the model, sucrose binds to a third, low-affinity binding site, allosterically changing the conformation of the active site so that dextran cannot be formed but acceptor products can be formed;Sugar mixtures containing isomaltodextrins were produced from sucrose using dextransucrase