Dextransucrase: studies on donor substrate specificity

Previous studies (D. S. Genghoff and E. J. Hehre, Proc. Soc. Exp. Biol. Med., 1972, 140, 1298–1301) have shown that an α-linked fluorine atom at C-1 of glucose provided sufficient activation to permit this analog to be a donor substrate for dextransucrase. In order to study the specificity at the donor substrate binding site, a series of α-1-fluorosugars have been synthesized. In kinetic experiments, it has been determined that they served as competitive inhibitors of sucrose, the natural substrate. A comparison of the K_i's provided information about the importance of specific changes in the glucose moiety with regard to binding to the enzyme. Similar kinetic studies were carried out with several β-1-fluorosugars, and the corresponding free monosaccharides. These were found to be noncompetitive inhibitors, and to bind poorly. The α-1-fluorosugars were also examined as donor substrates in reactions with known acceptors. With the exception of α-1-fluoroglucose, none of these analogs were active in this capacity.