Glucans, synthesis enzymes catalyzing

The situation is complicated by the fact that the efficiency of cellulose synthesis in the cell-free system is low, and the same enzyme preparation catalyzes the incorporation of D-glucosyl groups from UDP-Glc into alkali-soluble (1 - 2)-/3-D-glucans.370 A similar process was reported to occur with a membrane preparation of Rhizobium meliloti,371... 

Reaction 4.2 is catalyzed by starch synthase (E.C. 2.4.1.21 ADP-glucose 1,4-a-D-glucan 4-a-glucosyltransferase). Similar reactions are noted for glycogen synthesis in cyanobacteria and other bacteria,24 26 but the enzyme is referred to as glycogen synthase (also E.C. 2.4.1.21). 

Synthesis of the 1,6-a-D-glucose bonds in amylopectin is catalyzed by a branching enzyme [E.C. 2.4.1.18 1,4-a-D-glucan 6-a-(l,4-a-glucano)-transferase reaction 3]. Amylopectin contains longer chains (about 20-24 glucosyl units) and has less... 

Fig. 2 Main reactions catalyzed by sucrose-utilizing transglucosidases. The synthesis of a-glucans (Glc) linked through either a-1,6 a-1,3, a-1,4, or a-1,2 osidic linkages depending on the enzyme specificity is obtained by glucansucrases. The formation of a-D-glucose-1-phosphate from orthophosphate is obtained using sucrose-phosphorylases. The mechanism involves a double-inversion at the anomeric center via the formation of a covalent P-D-glucosyl enzyme intermediate...

The main reaction catalyzed by these enzymes is the synthesis of extracellular bacterial polysaccharides, a-glucans linked through different types of linkages and harboring distinct sizes and strucmres depending on the enzyme specificity and producing strain (Tables 1 and 2). Polymer elongation has been shown to proceed... 

The enzymes responsible for catalyzing the synthesis of dextrans and related polysaccharides form covalent glucose and polysaccharide complexes during synthesis of the glucans [76-79]. Using pulse and chase techniques with [U- " C] sucrose and L mesenteroides B-512FM dextransucrase, and 5. mutans 6715 dex-transucrase and mutansucrase immobilized on Bio-Gel P-2 beads, Robyt et al. [76,77] found that the polysaccharides were synthesized by the addition of glu-... 

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