Purification and characterization of a cytosolic broad specificity beta-glucosidase from human liver.

Abstract

A cytoplasmic beta-glucosidase has been isolated and purified 9,000-fold to homogeneity from the liver of a case of type 1 Gaucher's disease to a specific activity of 400,000 nmol/h/mg of protein. Although markedly elevated above control levels in this case of adult Gaucher's disease, the activity of this cytosolic liver enzyme was found to be markedly deficient in two cases of neurologic Gaucher's disease. The purification scheme employs QAE-Sephadex, DE52 cellulose, CM-Sephadex, hydroxylapatite, and Cibacron blue-Sepharose chromatography, and preparative isoelectric focusing. The beta-glucosidase preparations isolated from the liver of the case of adult Gaucher's disease and control liver have similar physical properties. Both enzymes have a molecular weight of approximately 53,000, sw,20 of 4.3, pI of 4.5-4.6, a pH optimum between 5 and 6, and a high affinity for 4-methylumbelliferyl-beta-D-glucopyranoside (Km = 0.06-0.07 mM). The enzymes from both sources also have a broad specificity and will hydrolyze the 4-methylumbelliferyl derivatives of beta-D-galactose, beta-D-fucose, beta-D-xylose, and alpha-L-arabinose in addition to several aryl-galactosides and steroid-glucosides. The cytoplasmic beta-glucosidase will not hydrolyze glucocerebroside and shows no cross-reactivity with antibodies prepared against lysosomal glucocerebrosidase. Both cytoplasmic beta-glucosidase and glucocerebrosidase will hydrolyze 17 beta-estradiol-17'-beta-D-glucose, and the activity of both enzymes on this substrate is increased more than 15-fold in the presence of the Gaucher spleen heat-stable factor. The role of this cytoplasmic beta-glucosidase in the etiology of Gaucher's disease and its possible relationship to lysosomal glucocerebrosidase are discussed.