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.