Biosynthesis of Dextrans and Related Polysaccharides

The mechanism for the polymerization of the teichoic acids has not been definitively established, but it is most probably very similar to the biosyntheses of the other lipid-coenzyme-dependent polysaccharides, the peptidomurein and Salmonella 0-antigen polysaccharide, in which the monomer unit or repeating unit attached to the lipid polyprenol pyrophosphate carrier is inserted between the growing chain and the lipid coenzyme carrier. See Fig. 10.12B for the proposed mechanism for teichoic acid biosynthesis. 

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- 

Reaction 1 acceptor transfer reaction to gi dextran chain branch 

B Two-site insertion mechanism for the biosynthesis of Streptococcus mutans alternating comb dextran by dextransucrase 

---