Mechanism of water-insoluble glucan synthesis in Streptococcus sobrinus.
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.
Takehara
T
T
Kyushu Dental College, Japan.
Ansai
T
T
Yamashita
Y
Y
Itoh-Andoh
M
M
Hanada
N
N
Kunimori
A
A
D005936:Glucans / Q000096:biosynthesis* / Q000737:chemistry; D005964:Glucosyltransferases / Q000378:metabolism*; D008745:Methylation; D016986:Streptococcus sobrinus / Q000378:metabolism*
D005936:Glucans; C036655:1,3-alpha-D-glucan synthase; D005964:Glucosyltransferases