Human alpha-fucosidase. Single residual enzymatic form in fucosidosis

Intrafamilial variability in fucosidosis

Two families with five patients affected with fucosidosis are described. Within each family, both type I and type II fucosidosis are present. This suggests that environmental factors or "modifying genes" different from the fucosidase structural gene contribute to the phenotype of a fucosidosis patient.

A thermolabile variant of alpha-L-fucosidase--clinical and laboratory findings

A family with two sibs affected clinically with the severe infantile form of fucosidosis is described. Biochemical studies revealed a relatively high residual activity (34-60% of normal) with markedly decreased thermostability. The importance of including thin layer chromatography for urinary oligosaccharides in the diagnostic workup for such patients is emphasized.

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.

pH-dependent association-dissociation of high and low activity plasma alpha-L-fucosidase

Population and family studies have confirmed the existence of a plasma alpha-L-fucosidase polymorphism in humans and the autosomal recessive inheritance of the low activity trait. The frequency of the latter is estimated at 11%. The low activity individuals or variants can also be distinguished by the fact that their plasma alpha-L-fucosidase is heat-inactivated at acidic pH. Sucrose gradient centrifugation results indicate the transition of non-variant plasma alpha-L-fucosidase with a molecular weight of 66,000 at pH 8.4 to an enzyme form with a molecular weight of 193,000 at pH 3.0. The former is thermolabile, the latter thermostable. Interconversion is pH-dependent. It is hypothesized that the non-variant enzyme, a monomer at alkaline pH, changes upon acidification into a trimeric conformation via dimerization. The thermolabile variant alpha-L-fucosidase monomer is not converted into a trimer, but only partially into a dimer.

Thermostability of human alpha-L-fucosidase. Relationship to fucosidosis and low-activity serum alpha-L-fucosidase

Thermostability studies have been performed at different preincubation temperatures (37-65 degrees C) on human alpha-L-fucosidase (alpha-L-fucoside fucohydrolase, EC 3.2.1.51), purified serum and liver enzyme, the isoelectric forms of purified liver enzyme which were separated by preparative isoelectric focusing, crude adult and fetal liver supernatant enzyme and neuraminidase-treated enzyme. Very different thermostability curves were found for the various isoelectric forms of alpha-L-fucosidase. The most neutral form (I) is least thermostable and the most acidic form (VIII) most thermostable, with the intervening forms (II-VII) having intermediate thermostabilities. For the isoelectric forms of liver alpha-L-fucosidase there appars to be a significant trend of increasing thermostability with increasing acidity (and presumably, increasing amounts of sialic acid). In order to determine what role, if any, sialic acid plays in determining the thermostability of alpha-L-fucosidase, comparative thermostability studies were performed on alpha-L-fucosidases from different human tissues which are reported to contain varying amounts of sialic acid. The purified sialic acid-rich serum enzyme is considerably more thermostable than the purified liver enzyme. The fetal liver enzyme (which is less acidic and may contain less sialic acid than the adult liver enzyme) is less thermostable than adult liver alpha-L-fucosidase. In contrast to all of the above findings which suggest that sialic acid confers thermostability to alpha-L-fucosidase, neuraminidase treatment of human liver alpha-L-fucosidase did not change its thermostability, even when considerable desialylation occurred as monitored by isoelectric focusing. The reason for these apparently inconsistent findings is not clear at the present time but several possible interpretations of the data are given.

Purification and characterization of alpha-L-fucosidase from the liver of a fucosidosis patient

alpha-l-Fucosidase was partially purified from the liver of a fucosidosis patient by column chromatography either on agarose-epsilon-aminohexanoylfucosamine or on concanavalin A-Sepharose, despite no apparent enzymic activity in the crude liver supernatant. Mixing studies indicated that the liver of the fucosidosis patient did not lack activators or contain inhibitors of alpha-l-fucosidase activity. The partially purified alpha-l-fucosidase from the liver of the fucosidosis patient exhibits a 4-5-fold-increased Michaelis constant for the 4-methylumbelliferyl substrate (700-750mum) and a greatly decreased thermostability at 55 degrees C compared with the normal liver enzyme. The pH-activity curve is similar to that for the normal enzyme between pH5 and 8, but quite dissimilar in the acid region (pH3.0-4.5): below pH4.5 the alpha-l-fucosidase shows no activity, whereas the normal enzyme retains considerable activity (>/=50% of maximal activity). Isoelectric focusing of the alpha-l-fucosidase revealed one major form with pI5.8 and other possible minor forms. No cross-reacting material was detected when the alpha-l-fucosidase was run in double-immunodiffusion experiments against the immunoglobulin-G fraction of anti-(alpha-l-fucosidase) antibodies, but the enzyme was immunoprecipitated by this immunoglobulin-G fraction. For at least the fucosidosis patient being studied here, all the data suggest retention of a thermolabile portion of normal alpha-l-fucosidase (with characteristic Michaelis constant and pH-activity curve) or production of a kinetically altered alpha-l-fucosidase with decreased catalytic activity but antigenic similarity to the normal enzyme.

Abnormal distribution of alpha-L-fucosidase in cystic fibrosis: decreased activity in serum

The activity of alpha-L-fucosidase is decreased in the serum of cystic fibrosis patients when compared to age-matched controls. This result, combined with the elevated activity in skin fibroblasts, supports the concept of an abnormal intracellular and extracellular distribution of alpha-L-fucosidase in cystic fibrosis.

Plasma acid hydrolases in normal adults and children, and in patients with some lysosomal storage diseases

Optimal assay conditions are described for plasma alpha-galactosidase, beta-glactosidase, beta-glucuronidase, alpha-mannosidase, alpha-glucosidase, N-acetyl-beta-glucosaminidase, alpha-fucosidase, N-acetyl-alpha-glucosaminidase, acid phosphatase and arylsulphatase A. The levels of these activities in normal adults and children, and the stabilities of the activities on storage at -20 degrees C or 4 degrees C, are reported. The levels of these enzymic activities in plasma from patients with Fabry, Pompe, Sanfilippo A, Sanfilippo B, Tay Sachs and Hunter diseases, GM1-gangliosidosis and metachromatic leucodystrophy are described, and the possibility of using plasma hydrolase activities in the diagnosis of these conditions is discussed.

Alpha-L-fucosidase in cultured bone marrow fibroblasts from fucosidosis patients

Bone marrow fibroblasts were cultured from two patients with fucosidosis type 2, six control subjects, and three patients with other lysosomal disorders. Optimal conditions for measuring alpha-L-fucosidase activity in lysates of these cells with the fluorogenic substrate 4-methylumbelliferyl-alpha-L-fucoside were established. The pH profile of normal bone marrow fibroblasts showed three peaks and a shoulder of enzymatic activity, with maximum activity at pH 4.75. In cells derived from fucosidosis patients two peaks of apparent alpha-L-fucosidase activity were obtained; the pH optimum was 4.5. alpha-L-Fucosidase activity (mean +/- SD) in the fucosidosis and control bone marrow fibroblasts was 2.5 and 312.4 +/- 10.9 nmoles 4-methylumbelliferone per milligram protein per hour, respectively. A reduction in the apparent specific enzymatic activity in the fucosidosis cells was observed by using increasing concentrations of cellular protein in the assay system. Mixing experiments between normal and fucosidosis cells gave the expected activities. These findings indicate that cultured bone marrow fibroblasts can be used for the diagnosis and study of fucosidosis.

Human alpha-fucosidase. Purification and properties

Human placental alpha-fucosidase (EC 3.2.1.51) has been extensively purified and partially characterized with respect to kinetic and structured properties. Although the enzyme seems to be separated by DEAE-cellulose chromatography in two forms which differ in their molecular weight and thermostability, an interconversion between the two forms takes place during storage and/or electrofocusing so that the same peaks of activity, revealed by the latter technique, are found before and after DEAE-cellulose chrome. The heterogeneous peaks of activity revealed by isoelectrofocusing show a reproducible pattern in the different tissues examined, except in serum where their pI values are consistently more acidic.