An enzyme from Streptococcus mutans forms branches on dextran in the absence of sucrose

An enzyme in glucosyltransferase preparations from Streptococcus mutans catalyzed the transfer of 14C]glucopyranoside from purified isomaltosaccharides, each containing 14C]glucopyranoside at its non-reducing terminus, to acceptor dextran, in the absence of sucrose. Half of the radioactivity present in the resulting 14C]dextrans was resistant to hydrolysis by amylo-1,6-glucosidase. Treatment of the 14C]dextrans with endodextranase resulted in extensive hydrolysis and produced 14C]-labeled limit oligosaccharides containing branch sites. Acetolysis of the 14C]-labeled limit oligosaccharides yielded 14C]nigerose, thus indicating the formation of branch sites on dextran in the absence of sucrose. The enzyme catalyzing this reaction has not been identified but appears to be independent of the major extracellular glucosyltransferases of S. mutans.