Sucrose glucosyltransferase

Sucrose and Dental Caries The most prevalent infection in humans worldwide is dental caries, which stems from the colonization and destruction of tooth enamel by a variety of acidifying microorganisms. These organisms synthesize and live within a water-insoluble network of dextrans, called dental plaque, composed of (al 6)-linked polymers of glucose with many (a 1 >3) branch points. Polymerization of dextran requires dietary sucrose, and the reaction is catalyzed by a bacterial enzyme, dextran-sucrose glucosyltransferase. 

Another extensively studied family of sucrose glucosyltransferases includes the extracellular enzymes from Leuconostoc and Streptococcus spp. Hehre (164) first indentified dextransucrase (sucrose 1,6-a-o-glucan 6-a-D-glucosyltransfer-ase, EC 2.4.1.5) in a culture supernatant of Leuconostoc mesenteroides and initiated structure and mechanism characterization. The enzyme became of practical interest because of the widespread application of dextran as a plasma support during World War II (165). Leuconostoc dextransucrase is sucrose induced (166), unlike the streptococcal enzymes (167), although expression of the latter varies considerably with culture conditions (168, 169). 

Similar covalent bonding is also involved in the action of the enzyme sucrose glucosyltransferase found in Pseudomonas saccharophila grown on sucrose medium. The normal reaction catalysed is... 

Various strains of oral streptococci produce D-glucosyltransferases which utilize sucrose as a o-glucosyl donor in the production of soluble and insoluble D-glucans. Consequently, it may be expected that some deoxyfluoro derivatives of sucrose function as competitive inhibitors for the dextransu-crases of tooth bacteria, thus preventing decay, or at least may be used as active-site probes for the enzymes. Another aim of these researches is to find non-metabolizable sweeteners. 

Mutans streptococci are the major pathogenic organisms of dental caries in humans. The pathogenicity is closely related to production of extracellular, water-insoluble glucans from sucrose by glucosyltransferase and acid release from various fermentable sugars. Poly(catechin) obtained by HRP catalyst in a phosphate buffer (pH 6) markedly inhibited glucosyltransferase from Streptococcus sorbrinus 6715, whereas the inhibitory effect of catechin for this enzyme was very low. 

This enzyme [EC 2.4.1.4], also referred to as sucrose-glucan glucosyltransferase, catalyzes the reaction of sucrose with a glucan (specifically, [(l,4)-o -D-glucosyl] ) to yield D-fructose and a longer glucan (that is, [(l,4)-o -D-glucosyl] +i). 

Another very valuable glycosyltransferase for the construction of well-defined polysaccharides is glucansucrase (dextransucrase systematic name sucrose (1 6)-a-D-glucan 6-a-D-glucosyltransferase EC 2.4.1.5). 

We have established a new aspect in nucleotide sugar synthesis by the application of sucrose synthase (UDPG D-fructose 2 glucosyltransferase, EC 2.4.1.13) the use of sucrose as a renewable resource for nucleotide sugar synthesis [273]. 

UDP-glucose-fructose glucosyltransferase. Sucrose-UDP UDP-glucose + D-fructose = UDP + sucrose,... 

The sucrose glycosyltransferases discussed in this section—sucrose phosphory-lase, B. subtilis levansucrase. Streptococcus glucosyltransferases, and Leuco-nostoc dextransucrase—share sucrose as a source of free energy in glucosyl or fructosyl transfer to an acceptor [ - 6600 cal/mol (146)]. The high specificity of the enzymes for sucrose has limited the variety of available substrates and consequently the extent of kinetic and mechanism analysis, although Chambert et al. (122) performed a remarkable series of kinetic experiments to establish the levansucrase kinetic mechanism. 

Sucrose phosphorylase (sucrose orthophosphate a-D-glucosyltransferase, EC 2.4.1.7) is distinguished as the first example of an experimentally trapped covalent enzyme intermediate complex, in this case a glucosyl-enzyme linked to a... 

Sucrose 3-a-glucosyltransferase, S. mutans (258) and Streptococcus downei (210) which have identical sequences in this peptide segment aspartic acid was labeled in the Streptococcus sobrinus enzyme (231). 

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