title: Difference in mode of inhibition between alpha-D-xylosyl beta-D-fructoside and alpha-isomaltosyl beta-D-fructoside in synthesis of glucan by Streptococcus mutans D-glucosyltransferase.
abstract: Both alpha-isomaltosyl beta-D-fructoside and alpha-D-xylosyl beta-D-fructoside show strong inhibition of the synthesis of water-insoluble and water-soluble D-glucans from sucrose by a partially purified preparation of a D-glucosyltransferase (GTase) from Streptococcus mutans 6715; however, the inhibitory modes differ substantially. In the presence of alpha-isomaltosyl beta-D-fructoside, the production of reducing sugars and the consumption of sucrose are remarkably enhanced, compared with a control of sucrose alone. Under these conditions, a large proportion of low-molecular-weight glycan (lmwg) and a series of nonreducing oligosaccharides (both containing D-fructosyl groups or residues) are produced. In contrast, in the presence of alpha-D-xylosyl beta-D-fructoside, the production of reducing sugars and the sucrose consumption are strikingly suppressed, and no lmwg or oligosaccharides are produced. Thus, it may be concluded that alpha-isomaltosyl beta-D-fructoside acts as an alternative acceptor for the D-glucosyl and/or D-glucanosyl transfer reactions of the enzyme, and serves to lessen the formation of insoluble and soluble D-glucan, although it stimulates the transferring activity of the enzyme. On the other hand, alpha-D-xylosyl beta-D-fructoside competitively inhibits the sucrose-splitting activity of the enzyme as an analog to sucrose, and thereby diminishes the synthesis of D-glucan.
mesh_terms: D004187:Disaccharides / Q000494:pharmacology*; D005936:Glucans / Q000096:biosynthesis*; D005964:Glucosyltransferases / Q000037:antagonists & inhibitors* / Q000302:isolation & purification; D007700:Kinetics; D009844:Oligosaccharides / Q000032:analysis; D013295:Streptococcus mutans / Q000201:enzymology*; D013329:Structure-Activity Relationship; D014312:Trisaccharides / Q000494:pharmacology*
chemical_list: D004187:Disaccharides; D005936:Glucans; D009844:Oligosaccharides; D014312:Trisaccharides; C043602:xylosylfructoside; C048721:isomaltosylfructoside; D005964:Glucosyltransferases