Major isomaltase (alpha-1,6-glucosidase) required for isomaltose utilization. Preferentially hydrolyzes isomaltose, palatinose, and methyl-alpha-glucoside, with little activity towards isomaltotriose or longer oligosaccharides. Does not hydrolyze maltose. Hydrolysis of (1->6)-alpha-D-glucosidic linkages in some oligosaccharides produced from starch and glycogen by alpha-amylase, and in isomaltose. Expression is increased in response to the addition of maltose, isomaltose, and alpha-methylglucopyranoside. Present with 752 molecules/cell in log phase SD medium. Belongs to the glycosyl hydrolase 13 family.