2 IMMUNOLOGICALLY DISTINCT HUMAN ACIDIC BETA-GALACTOSIDASE-A ISOZYMES

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  • 1 January 1977
    • journal article
    • research article
    • Vol. 22  (4) , 276-282
Abstract
Two acidic .beta.-galactosidase [EC 3.2.1.23] isozymes (designated A1 and A2) were separated by isoelectric focusing from .beta.-galactosidase A of human liver. Kinetic studies with 4-methylumbelliferyl-.beta.-D-galactopyranoside substrate revealed similar parameters for both. The Km value was 0.32 mmol/l for A1 and 0.30 mmol/l for A2 and Vmax values of 59.3 and 59.4 .mu.mol min-1 mg-1, respectively. The pH optimum was 4.2 for .beta.-galactosidase A1 and 4.5 for the A2 form. The A1 enzyme form was shown to be more heat labile than the A2. Significant differences were observed with antibody preparations against the 2 enzyme forms. Using the anti-A1 antibodies, 2 precipitin arcs with residual enzymatic activity were obtained by immunoelectrophoresis of .beta.-galactosidase A whereas only 1 was obtained with anti-A2 antibodies. Anti-A1 precipitated 85% of the original activity present in .beta.-galactosidase A and only 56% could be precipitated by anti-A2. The possibility of common structural components is suggested.