Mechanisms in the glucansucrase synthesis of polysaccharides and oligosaccharides from sucrose

This chapter examines the mechanisms involved in the glucansucrase synthesis of polysaccharides and oligosaccharides from sucrose. The enzymes that catalyze the synthesis of glucans from sucrose are secreted into the culture medium. The enzymes produced by Leuc. mesenteroides strains are inducible by sucrose, which is absolutely required in the culture media for their production. The glucansucrases use sucrose as a high-energy glucosyl donor for polysaccharide and oligosaccharide syntheses. For glucan synthesis, the energy of the glucose glycosidic linkage of sucrose must be conserved until the glucose is incorporated into the polysaccharide. In addition, the glucose moiety must be manipulated so that the enzyme can perform its catalytic function of synthesizing a glycosidic bond. This can be achieved by the transfer of the glucose moiety of sucrose to the enzyme with the formation of a covalent, high-energy-enzyme intermediate. The two-site insertion mechanism for the de Novo synthesis of polysaccharide by the addition of glucose to the reducing end is also elaborated in the chapter. © 1995 Academic Press, Inc.