Biochemical studies on an unusual case of fucosidosis.

Biochemical studies have been performed on the spleen and liver of a patient suspected of having fucosidosis. The specific, complete deficiency of 4-methylumbelliferyl (4-MU)-α-L-fucosidase activity coupled with the massive liver accumulation of polar glycolipids (comparable to those found in a known case of fucosidosis), confirms the diagnosis of fucosidosis. The patient is unusual in that his liver retains 25–50 % of normal α-L-fucosidase activity for the p-nitrophenyl (PNP) substrate. The patient's spleen showed complete deficiency of α-L-fucosidase activity for both 4-MU- and PNP-α-L-fucopyranoside. The patient's crude liver α-L-fucosidase was not significantly different in thermostability when compared to the crude enzyme from a normal liver. After partial purification on agarose-ɛ-aminocaproyl-fucosamine and sepharose-concanavalin A, the patient's liver α-L-fucosidase was found to possess both PNP and 4-MU activities. This suggests that components in the patient's crude liver supernatant may inhibit 4-MU-α-L-fucosidase activity. This was demonstrated further when the patient's liver supernatant was found to inhibit significantly normal liver 4-MU-α-L-fucosidase activity. Kinetic and immunochemical characterization indicated that the patient's α-fucosidase was similar, if not identical, to the normal liver enzyme. Apparent Km's for 4-MU-α-L-fucopyranoside were determined to be 0.1 mM and 0.12 mM for the patient and normal liver enzyme, respectively. The IgG fraction of antiserum prepared against purified normal liver α-L-fucosidase immunoprecipitated 81 % of the patient's α-L-fucosidase, suggesting similarity of antigenic determinants.