Beta-Glucoside Hydrolase Activity of Normal and Glucosylceramidotic Cultured Human Skin Fibroblasts

Cultured human skin fibroblasts from normal and glucosylceramidotic subjects are found to contain one beta-glucoside hydrolase as compared with multiple enzymes in other tissues. The fibroblast enzyme has an approximate molecular weight of 150,000 under isotonic conditions, as determined by gel filtration. It occurs as a large aggregate at low ionic strength. Ceramide, 4-methylumbelliferyl, and p-nitrophenyl beta-glucosides are active as substrates. The enzyme in whole cell homogenates is membrane-bound and is solubilized by a combination of Triton X-100 and sodium taurocholate. It has a pH optimum at 4.2 and no demonstrable divalent cation requirement. The cultured fibroblast beta-glucosidase displays close similarity to one of the forms of beta-glucosidase in human spleen, specifically that form which is affected in Gaucher's disease. 4-Methylumbelliferyl beta-glucosidase activity in homozygous fibroblasts from infantile and adult forms of Gaucher's disease are reduced to 9 and 14%, respectively, of normal fibroblast activity. The residual activity in the lipidotic cells shows increased heat lability, but cannot be distinguished from that in normal cells with respect to gel exclusion properties, Michaelis constant, and pH dependence.