Detailed Action Mechanism of Dextrin Dextranase from Acetobacter capsulatus ATCC 11894

The detailed action mechanism of dextrin dextranase (EC 2.4.1.2, DDase) from Acetobacter capsulatus ATCC 11894 was investigated. DDase catalyzed the transglucosylation action of the non-reducing terminal glucosyl residue of a donor substrate, and three transglucosylation modes were recognized; (1) transfer of an α-1,4 linked glucosyl residue forming an α-1,6 linkage, (2) transfer of an α-1,4 linked glucosyl residue forming an α-1,4 linkage, (3) transfer of an α-1,6 linked glucosyl residue forming an α-1,6 linkage. From these results, the action of DDase was considered to transfer α-1,4 or α-1,6 linked glucosyl residues at non-reducing termini of oligosaccharides to glucose molecules or glucosyl residues at non-reducing termini of other oligosaccharides forming α-1,4 or α-1,6 linkages. As the α-1,6 linked terminal glucosyl residues were less reactive than α-1,4linked terminal glucosyl residues, DDase accumulated the α-1,6linked glucosyl residues, which is dextran.