title: Mechanism of water-insoluble glucan synthesis in Streptococcus sobrinus.
abstract: Synthesis of water-insoluble glucan (IG) by 1,3-alpha-D-glucan synthase from Streptococcus sobrinus was examined using methylation analysis. The purified enzyme was incubated with sucrose and dextran T2000 (DT2000) for a given time and only IG was harvested by centrifugation. The remaining supernatant was incubated again, and IG was obtained. By repeating the above method using the residual supernatant, we obtained 5 varieties of IG precipitated in different periods. These IGs were methylated and examined using gas chromatograph mass spectrometry. The DT2000 water-insolubilized in the early reaction stage tended to have a highly ramified structure, with 1,3-alpha-D-glucan on a 1,6-alpha-D-glucan chain as the main chain. On the contrary, the DT2000 water-insolubilized in the late stage tended to have sparse side chains of 1,3-alpha-D-glucan which elongated with incubation. Specifically, the greater the number of side chains, the sooner the DT2000 was insolubilized. These results suggest that water-insolubilization of the water-soluble glucan not only depends on the increase of the ratio of 1,3-alpha-glucoside linkages to 1,6-alpha-glucoside linkages but also on the degree of branching of the 1,3,6-alpha-branched glucoside linkages.
authors.affiliation: Kyushu Dental College, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Takehara
authors.forename: T
authors.initials: T
authors.lastname: Ansai
authors.forename: Y
authors.initials: Y
authors.lastname: Yamashita
authors.forename: M
authors.initials: M
authors.lastname: Itoh-Andoh
authors.forename: N
authors.initials: N
authors.lastname: Hanada
authors.forename: A
authors.initials: A
authors.lastname: Kunimori
mesh_terms: D005936:Glucans / Q000096:biosynthesis* / Q000737:chemistry; D005964:Glucosyltransferases / Q000378:metabolism*; D008745:Methylation; D016986:Streptococcus sobrinus / Q000378:metabolism*
chemical_list: D005936:Glucans; C036655:1,3-alpha-D-glucan synthase; D005964:Glucosyltransferases