A gene regulating the time dependence of alpha-L-fucosidase concentration is closely linked with the structural gene in man

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.

Biosynthesis, processing, and extracellular release of alpha-L-fucosidase in lymphoid cell lines of different genetic origins

In humans, the quantity of alpha-L-fucosidase in serum is determined by heredity. The mechanism controlling levels of the enzyme in serum is unknown. Lymphoid cell lines derived from individuals with either low, intermediate, or high alpha-L-fucosidase in serum were established. Steady-state levels of intracellular and extracellular alpha-L-fucosidase as well as rates of synthesis and secretion of enzyme overlapped among the cell lines. Thus, in vivo serum phenotypes were not expressed in this system. No appreciable differences in the qualitative processing of newly made alpha-L-fucosidase were observed among these lymphoid cell lines. Cells pulse-labeled with 35S-methionine from 0.25 to 2 hr had an intracellular form of enzyme with a Mr = 58,000. Cells pulsed for 1.5 hr and chased for 21 hr with unlabeled methionine had an intracellular form of Mr = 60,000 and an extracellular form of Mr = 62,000. All three enzyme forms were glycoproteins with a common polypeptide chain of Mr = 52,000 but with different carbohydrate moieties. No evidence for a high molecular mass precursor form of alpha-L-fucosidase was found. Fucosidosis is a rare, inherited disease in which alpha-L-fucosidase activity in tissues and body fluids is low or absent. The mutations for fucosidosis and the serum polymorphism map separately. Lymphoid cells from two siblings with fucosidosis had 8-fold to 341-fold less intracellular alpha-L-fucosidase protein with 11-fold to 56-fold lower specific activities than control cells. Residual mutant enzyme was a glycoprotein with a polypeptide chain virtually the same size (Mr = 52,000) as control enzyme. However, residual mutant enzyme was hypoglycosylated and hypersecreted as compared to control enzyme.

Variation in alpha-L-fucosidase properties among 28 inbred mouse strains: six strains have high enzyme activity and heat-stabile enzyme with a variant pH-activity curve; twenty-two strains have low activity and heat-labile enzyme

Alpha-L-fucosidase in tissues of 28 inbred mouse strains varied with respect to three properties: high or low heat stability, a pH-activity curve with high or low relative activity at pH 2.8, and high or low activity. Alpha-L-fucosidase from six strains (A/J, BDP/J, LP/J, P/J, SEA/GNJ, and 129/J) had high heat stability, high pH 2.8 relative activity, and high activity, whereas the other 22 strains all had low heat stability, low pH 2.8 relative activity, and low activity. The heat-stability difference was seen in all organs tested (brain, liver, kidney, spleen, heart, skeletal muscle, lung, and testis) for two heat-stabile strains (P/J and 129/J) and four heat-labile strains (C57BL/6J, C3H/HeJ, DBA/2J, and BALB/cJ) studied in detail. The findings suggested that two structural variants of alpha-L-fucosidase, probably genetically determined, exist in these 28 inbred mouse strains, although the presence of linkage disequilibrium between alleles of tightly linked structural and regulatory genes could not be excluded.