A microassay for acid beta-galactosidase activity toward asialofetuin.

To study the enzymatic properties of beta-galactosidase from the patients with a beta-galactosidase deficiency such as GM1 gangliosidosis, determination of enzymatic activity with naturally occurring substrates, asialofetuin in addition to another natural substrate, GM1 ganglioside, is essentially required. With a previously reported, simple and sensitive fluorometric assay for GM1 ganglioside beta-galactosidase using high performance liquid chromatography (HPLC), optimal reaction conditions were determined for the assay of acid beta-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 GM1 gangliosidoses and mucopolysaccharidosis IV-B (Morquio B syndrome). This method was applicable to study of the enzymatic properties of the mutant beta-galactosidase and provided an alternative to assays employing radioactive or artificial substrates.