Purification and characterization of α-l-fucosidase from the liver of a fucosidosis patient

Abstract

α-l-Fucosidase was partially purified from the liver of a fucosidosis patient by column chromatography either on agarose–ε-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 α-l-fucosidase activity. The partially purified α-l-fucosidase from the liver of the fucosidosis patient exhibits a 4–5-fold-increased Michaelis constant for the 4-methylumbelliferyl substrate (700–750μm) and a greatly decreased thermostability at 55°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 α-l-fucosidase shows no activity, whereas the normal enzyme retains considerable activity (≥50% of maximal activity). Isoelectric focusing of the α-l-fucosidase revealed one major form with pI5.8 and other possible minor forms. No cross-reacting material was detected when the α-l-fucosidase was run in double-immunodiffusion experiments against the immunoglobulin-G fraction of anti-(α-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 α-l-fucosidase (with characteristic Michaelis constant and pH–activity curve) or production of a kinetically altered α-l-fucosidase with decreased catalytic activity but antigenic similarity to the normal enzyme.