A microassay for acid β-galactosidase activity toward asialofetuin

To study the enzymatic properties of β-galactosidase from the patients with a β-galactosidase deficiency such as G_M1 gangliosidosis, determination of enzymatic activity with naturally occurring substrates, asialofetuin in addition to another natural substrate, G_M1 ganglioside, is essentially required. With a previously reported, simple and sensitive fluorometric assay for G_M1 ganglioside β-galactosidase using high performance liquid chromatography (HPLC), optimal reaction conditions were determined for the assay of acid β-galactosidase activity toward asialofetuin in skin fibroblast homogenates. Under these conditions, reduced enzymatic activities could be detected in cultured skin fibroblasts from patients with type 1 and 3 G_M1 gangliosidoses and mucopolysaccharidosis IV-B (Morquio B syndrome). This method was applicable to study of the enzymatic properties of the mutant β-galactosidase and provided an alternative to assays employing radioactive or artificial substrates.