SDS-PAGE of the purification of high-pI α-glucosidase. Lane 1, Ammonium sulfate precipitate (640 μg); lane 2, DEAE Fractogel (135 μg); lane 3, COO− Fractogel, pH 5.5 (20 μg); lane 4, rechromatography (12.4 μg); lane 5, butyl-Sepharose (1.3 μg); and lane 6, COO− Fractogel, pH 7.3 (1.2 μg). M, Marker proteins.