Abstract
An assay procedure was developed for accurate estimation of lactosylceramidase II in the presence of relatively high activity of lactosylceramidase I. The procedure involves determination of lactosylceramide-cleaving activities under two different assay conditions, and lactosylceramidase II activity is calculated by the difference. Applicability of the procedure was evaluated with separated soluble fractions of the two beta-galactosidases from normal human brains, and with whole homogenates of gray and white matter, liver and cultured fibroblasts from control individuals and from patients with globoid cell leukodystrophy or GM1-gangliosidosis. The use of the lactosylceramidase I assay procedure developed by Wenger, D.A., Sattler, M., Clark, C. and McKelvey, H. ((1974) Clin. Chim. Acta 56, 199-206) and of the present procedure permits accurate diagnosis of both globoid cell leukodystrophy and GM1-gangliosidosis with one natural substrate, lactosylceramide, irrespective of the relative proportion of the two beta-galactosidases in the tissue.