Dextranase is an enzyme that specifically breaks down dextran, which is a polysaccharide made of glucose units linked mainly by α-1,6-glycosidic bonds. It hydrolyzes the α-1,6 glycosidic linkages in dextran, producing smaller sugars like isomaltose and glucose. It does not act on other glucose polymers like starch (amylose/amylopectin) efficiently because their linkages differ.