Purification and Characterization of an Oligo-isomaltosaccharide Synthase from a Streptococcus sobrinus Glucosyltransferase-I Deficient Mutant

One glucosyltransferase (GTF)-I deficient mutant of Streptococcus sobrinus strain B13N was isolated through chemical mutagenesis with ethyl methanesulfonate, and characterized. This mutant, designated as B13N-Id, readily allowed us to purify a homogeneous oligo-isomaltosaccharide synthase (GTF-S) from its culture fluid. The purified GTF-S was only recognized with rabbit polyclonal antibody against recombinant GUT-S from an Ecsherichia coli MD124 clone expressing the B13N gtfS gene, and showed the almost same enzymatic properties as the recombinant enzyme. A double reciprocal plot of the B13N GTF-S for sucrose was biphasic, and the affinity for this substrate was high compared to that of GTF-S enzymes from other strains.