Hydrolysis of natural and synthetic substrates by alpha-L-fucosidase, beta-D-glucuronidase and beta-N-acetylhexosaminidase purified from molluscs

Mammalian alpha-L-fucosidases

Mammalian alpha-L-fucosidases are a ubiquitous group of relatively large multimeric lysosomal glycosidases involved in the degradation of a diverse group of naturally-occurring fucoglycoconjugates. These enzymes are closely related structurally as indicated by immunochemical cross-reactivity and cloning studies. Mammalian fucosidases are sialoglycoproteins and the carbohydrate, particularly sialic acid, contributes to producing multiple isoforms which can differ in various species as well as in different tissues within a given species. alpha-L-Fucosidases exhibit maximal activity at pH values between 4 and 7, have similar kinetic properties with synthetic substrates (PNP-fucoside and 4-MU-fucoside), and exhibit broad substrate specificity on natural substrates. Numerous linkages (alpha 1-2, alpha 1-3, alpha 1-4, alpha 1-6), primarily to galactose and N-acetylglucosamine, can be hydrolyzed but preference is often seen for small mol. wt water-soluble substrates with fucose in alpha 1-2 linkage to galactose. The importance of alpha-L-fucosidase in mammalian metabolism is evidenced by deficiency or absence of its enzymatic activity leading to a fatal genetic disease, at least in humans and English Springer Spaniels.

On the specificity of the two forms of human serum alpha-L-fucosidase

All normal sera exhibiting either normal or low activities contain two forms of alpha-L-fucosidase (F1 and F2). These two forms, isolated from either type of serum, have respectively similar properties, but the low-activity sera contain a major proportion of the thermolabile, less-acidic form, F1. The specificities for natural substrates (glycoproteins and oligosaccharides) and for synthetic fucosides have been studied. All types of alpha-L-fucosidase linkages (1,2; 1,3; 1,4 and 1,6) are split by the form F2. The specificity of the form F1 is more restricted. Only alpha(1,3) and some types of alpha(1,2) and alpha(1,4) fucosyl linkages are split.