Purification and properties of two forms of human alpha-L-fucosidase

High (100 000) and low (50 000) molecular weight forms of alpha-L-fucosidase (alpha-fucosidase I and II) were purified to apparent homogeneity from human spleen, liver brain and kidney on the basis of differential affinity for epsilon-amino-caproyl fucosamine-agarose bead columns. Alpha-fucosidase I (the "bound" form) consisted of two 50 000 dalton monomers; however, both forms can aggregate to tetramer and hexamer forms. Most previous studies on alpha-fucosidase have been carried out on this form of human alpha-fucosidase although the bound and unbound forms of the enzyme were present in equal amounts in human spleen. The bound (100 000) form is a sialoglycoprotein whereas the unbound (50 000) form, is a neutral mannose-rich glycoprotein. Other differences with respect to amino acid composition, pH optimum, electrophoretic mobility, KM, thermal stability, and natural substrate specificities were observed. All preparations hydrolysed 4-methylumbelliferyl-alpha-L-fucoside, flucosyllactose, and lacto-N-fucopentaose I, but the unbound fraction (alpha-fucosidase II) preferentially hydrolyused lacto-N-fucopentaose II. The unbound (mannose-rich) alpha-fucosidase II was taken up by human skin fibroblasts with higher affinity (5% per 2 h per 2 times 10(5) cells) than the bound (sialo-) alpha-fucosidase I (<1% per 2 times 10(5) cells). Uptake was inhibited by other lysosomal hydrolases, fetal calf serum, mannose 6-phosphate and phosphomannans and to a lesser extent by heparins. Our studies suggest that alpha-fucosidase I is not a simple dimer of alpha-fucosidase II and represents a less-biologically active form of the enzyme.