Alpha-L-fucosidase in cultured bone marrow fibroblasts from fucosidosis patients

Radioimmunoassay determination of decreased amounts of alpha-L-fucosidase protein in fucosidosis

Purified human liver alpha-L-fucosidase (EC 3.2.1.51) has been radioiodinated by a chloramine-T procedure to a specific activity of 3.7 . 10(6) dpm/micrograms protein without altering its apparent Michaelis constant for the 4-methylumbelliferyl substrate. This 125I-labeled alpha-L-fucosidase has been used in development of a competitive binding radioimmunoassay for alpha-L-fucosidase which can detect 1-2 ng of enzyme protein and has been employed to quantify the amount of alpha-L-fucosidase protein in the liver and spleen from a patient with fucosidosis. Less than 1% of the normal amount of alpha-L-fucosidase protein is present suggesting that normal amounts of catalytically inactive alpha-L-fucosidase are not found in this disease.

Purification and characterization of alpha-L-fucosidase from the liver of a fucosidosis patient

alpha-l-Fucosidase was partially purified from the liver of a fucosidosis patient by column chromatography either on agarose-epsilon-aminohexanoylfucosamine or on concanavalin A-Sepharose, despite no apparent enzymic activity in the crude liver supernatant. Mixing studies indicated that the liver of the fucosidosis patient did not lack activators or contain inhibitors of alpha-l-fucosidase activity. The partially purified alpha-l-fucosidase from the liver of the fucosidosis patient exhibits a 4-5-fold-increased Michaelis constant for the 4-methylumbelliferyl substrate (700-750mum) and a greatly decreased thermostability at 55 degrees C compared with the normal liver enzyme. The pH-activity curve is similar to that for the normal enzyme between pH5 and 8, but quite dissimilar in the acid region (pH3.0-4.5): below pH4.5 the alpha-l-fucosidase shows no activity, whereas the normal enzyme retains considerable activity (>/=50% of maximal activity). Isoelectric focusing of the alpha-l-fucosidase revealed one major form with pI5.8 and other possible minor forms. No cross-reacting material was detected when the alpha-l-fucosidase was run in double-immunodiffusion experiments against the immunoglobulin-G fraction of anti-(alpha-l-fucosidase) antibodies, but the enzyme was immunoprecipitated by this immunoglobulin-G fraction. For at least the fucosidosis patient being studied here, all the data suggest retention of a thermolabile portion of normal alpha-l-fucosidase (with characteristic Michaelis constant and pH-activity curve) or production of a kinetically altered alpha-l-fucosidase with decreased catalytic activity but antigenic similarity to the normal enzyme.