Monoclonal antibodies were obtained against the membrane‐bound lysosomal enzyme β‐glucocerebrosidase (acid β‐glucosidase), which is deficient in Gaucher's disease. BALB/c mice were immunized with homogeneous enzyme protein extracted from a sodium dodecyl sulphate/polyacrylamide gel. The mice were subsequently hyperimmunized with partially purified enzyme prior to fusion of spleen cells with myeloma cells. After fusion, 32 primary hybrid cell populations were obtained which continued to produce antibodies against β‐glucocerebrosidase after prolonged time of culture. All antibodies reacted with both native and denatured enzyme. Four primary cell populations were subcloned and the antibodies produced were characterized. The antibodies were all four of the IgG1 subclass. Three of these antibodies bind to protein A whereas one does not. The results of binding assays indicated that three of the antibodies react with the same antigenic domain (epitope 1), but the fourth with a different one (epitope 2). Probably two antigenic determinants are present in epitope 1 since one of the antibodies with specificity for epitope 1 is inactivated after iodination by the chloramine‐T procedure whereas a second one is not.

When isolated rat-liver cells were incubated for 1 min at 37 "C with filipin at a concentration of 50 pM, the plasma membrane became permeable to sucrose. inulin, glycerol 3-phosphate and other low-molecular-weiglit compounds. Upon removal of the filipin and subsequent incubation of the cells at 37°C there was a gradual leakage of lactate dehydrogenase from the cells. However, the leakage of lactate dehydrogenase could be prevented for about 10 niin by including glutathione and ATP in the incubation medium.The filipin-treated cells were able to metabolize phosphorylated sugars. The conversion of fructose 1,6-bisphosphate to fructose 6-phosphate, glucose 6-phosphate and glucose was inhibited by AMP but not by high concentrations of fructose 1,6-bisphosphate. The results indicate that filipin-treated cells can be used to study the kinetic parameters of enzymes in their macromolecular environment in situ.