Lactosyl ceramidosis: Deficient activity of neutral β-Galactsidase in liver and cultivated fibroblasts?

Neutral β-galactosidase was partially purified from liver of normal controls, a patient with Niemann-Pick disease type A and the previously described patient with lactosyi ceramidosis using Concanavalin A-Sepharose adsorption and Sephadex G-100 gel filtration. The partially purified fractions were essentially free of galactosyl ceramide β-galactosidase and GM₁ β-galactosidase activities. The normal and Niemann-Pick fractions were found to hydrolyze lactosyl ceramide, in the presence of sodium taurodeoxycholate, at a pH optimum of 5.6 as well as aryl β-galactosides and aryl β-glucosides at pH 6.2. The corresponding fraction from the lactosyi ceramidosis liver contained only 1-4% of the normal activity towards artificial substrates and lactosyl ceramide. Cross-reacting material identical to the normal was demonstrated in this fraction with antiserum raised against purified neutral β-galactosidase, but no activity was observed in the precipitin line when stained with naphthol AS-LC-β-galactoside or naphthol AS-LC-β-glucoside. A similar deficiency of neutral β-galactosidase activity was demonstrated in cultivated fibroblasts of the patient with lactosyl ceramidosis. Following adsorption on Concanavalin A-Sepharose and anti-GM₁ β-galactosidase antibody Sepharose conjugates and chromatography on DEAE cellulose, fibroblast lysates from the patient exhibited 3% of normal activity towards 4-methylumbelliferyl β-glucoside at pH 6.2 and 12% of normal activity towards lactosyl ceramide at pH 5.6. These data suggest that neutral β-galactosidase may have an in vivo role in the cleavage of lactosyl ceramide and that a deficiency of this activity may be related to the lactosyl ceramide accumulation observed in the patient with lactosyl ceramidosis.