STRUCTURE OF THE LINEAR, LOW-MOLECULAR-WEIGHT DEXTRAN SYNTHESIZED BY A D-GLUCOSYLTRANSFERASE (GTF-S3) OF STREPTOCOCCUS-SOBRINUS

Four extracellular alpha-D-glucosyltransferases (GTF) have been separated from cultures of Streptococcus sobrinus strains grown in continuous culture. Three of the GTF synthesized soluble dextrans from sucrose, and one of these enzymes, GTF-S3, catalysed the production of a low molecular weight, linear dextran. Methylation analysis and high field proton NMR spectroscopy on the intact S3 glucans confirmed that these dextrans were small (dp 20-30) and linear, with the majority of chains terminated with a sucrosyl moiety. Enzymic hydrolysis, followed by analytical and semi-preparative HPLC, led to the isolation of only linear oligosaccharides, one of which was identified as 6G-glucosylsucrose. The results are accommodated by the two-site insertion mechanism for dextran synthesis proposed by Robyt et al. (1974) (Arch. Biochem. Biophys., 165, 634).