Human serum alpha-L-fucosidase

The effect of blood sampling and preanalytical processing on human N-glycome

Glycome modulations have been described in the onset and progression of many diseases. Thus, many studies have proposed glycans from blood glycoproteins as disease markers. Astonishingly, little effort has been given unraveling preanalytical conditions potentially influencing glycan analysis prior to blood biomarker studies. In this work, we evaluate for the first time the effect of hemolysis, storage and blood collection, but also influence of various times and temperatures between individual processing steps on the total N-glycome and on a glycan-biomarker score. Venous blood was collected from 10 healthy donors in 11 blood collection tubes with different additives, processed variously to obtain 16 preanalytical variables and N-glycans released from serum or plasma were analyzed by MALDI-TOF-MS and capillary electrophoresis coupled with fluorescence detection (CE-LIF) for the first time. Long time storage of deep frozen samples at -20°C or -80°C exerted only a minor influence on the glycome as demonstrated by CE-LIF. The N-glycome was very stable evidenced by MALDI-TOF when stored at 4°C for at least 48 hours and blood collected in tubes devoid of additives. The glycome was stable upon storage after centrifugation and aliquoting, which is an important information considering future diagnostic applications. Hemolysis, however, negatively correlated with an established glycan score for ovarian cancer, when evaluated by MALDI-TOF-MS measurement by affecting relative intensities of certain glycans, which could lead to false negative / positive results in glycan biomarker studies.

Modulation of expression in BEAS-2B airway epithelial cells of α-L-fucosidase A1 and A2 by Th1 and Th2 cytokines, and overexpression of α-L-fucosidase 2

Chronic Th2-driven airway inflammation with excessive mucus production occurs in asthma. The regulation of FUCA1 and FUCA2 gene expression and enzyme activity in response to asthma-associated Th2 cytokines and, for contrast, Th1 cytokine IFN-γ, were investigated in a human airway cell line. BEAS-2B cells were supplemented with Th2-derived cytokines (IL-13, IL-4, IL-5) or/and IFN-γ. RNA and cell supernatants from stimulated and unstimulated cells were collected over a period of 3 h. Alpha-L-fucosidase A1 and A2 gene expression were assessed using real time RT-PCR, while enzymatic activities were measured using a fluorescent assay. To characterise α-L-fucosidase A2, CHO-K1 and BEAS-2B cell lines were transiently transfected, the FUCA2 gene was overexpressed, and the protein was immunoprecipitated. The transcription of FUCA1 was upregulated (p < 0.01) in response to IFN-γ, suggesting that FUCA1 transcription and fucosidase activity are regulated in a Th1-dependent manner. The gene expression was the highest for 30 min after IFN-γ stimulation (>twofold induction), whereas secreted enzyme activity in BEAS-2B cells was significantly increased 1 h after IFN-γ addition. IL-4, IL-5 and IL-13 had no effect on FUCA1 and FUCA2 expression and activity. The IFN-γ-induced increase in expression and activity was repressed by the presence of the Th2 cytokine IL-5. Enzymatically active α-L-fucosidase 2 was immunoprecipitated from BEAS-2B cells, with highest activity at pH 4.9. IL-13, IL-4 and IL-5 have no effect on the expression of FUCA1 and FUCA2, but its expression is upregulated by IFN-γ, a Th1 cytokine. Active α-L-fucosidase 2 was overexpressed in BEAS-2B cells.

Purification and characterization of α-L-fucosidase from human primary hepatocarcinoma tissue

AIM: To purify and characterize α-L-fucosidase from human liver cancer tissue and to detect the localization of α-L-fucosidase in tumor tissue.

METHODS: Cation exchange chromatography on CM-52 and ultrafiltration were used to separate α-L-fucosidase (AFU) from crude extract of liver cancer tissue. 4-methylumbelliferyl-α-L-fucopyranoside was used as a fluorescent substrate to quantify the purified AFU activity in each step. A polyclonal antibody (pAb) against the purified AFU was obtained by anion exchange chromatography on DEAE-52 after ammonium sulfate fractionation and ultrafiltration. Immuohistochemical staining was used to observe the expression of AFU in malignant and adjacent liver tissues.

RESULTS: Human α-L-fucosidase was purified 74–fold to apparent homogeneity with 15% yield. SDS-PAGE indicated the presence of one subunit of molecular weight of 55 Ku. The specific activity of AFU in pooled fraction by chromatography was 10085 IU/mg. Western blot analysis indicated that the pAb could recognize one protein band of molecular weight of 55 Ku. The expression of AFU was observed in cytoplasm membrane of liver cancer tissue but not in that of adjacent tissue.

CONCLUSION: The purified α-L-fucosidase from primary hepatocarcinoma (PHC) is different in its properties from α-L-fucosidase in human other organs. The polyclonal antibody prepared in this experiment can be applied to the diagnosis of PHC.

Characterization of the oligosaccharides of plasma sex hormone binding globulin from noncirrhotic alcoholic patients

In previous reports we have demonstrated high plasma levels of sex hormone-binding globulin (SHBG) in asymptomatic alcoholic men. In the present work the physicochemical properties of SHBG from plasma of noncirrhotic alcoholic patients have been further compared with SHBG of control subjects. Steroid binding to SHBG was similar for the two groups: alcoholic men, K(d) of 0.62 +/- 0.07 nM and control individuals, K(d) of 0.70 +/- 0.10 nM. The structure of oligosaccharides attached to SHBG from controls and alcoholic men were determined by using serial chromatography. Our data indicated that 7% of SHBG of control individuals was not retarded by the Con-A column, whereas approximately 30% of SHBG of alcoholic men eluted in the void volume of Con A. Approximately 46% of SHBG of alcoholics applied to Con A, possessed biantennary complex oligosaccharides, as indicated by the fact that it could be eluted with methyl-alpha-D-glucopyranoside and by its retention on wheat germ agglutinin; in contrast, when SHBG from control men was analyzed, approximately 51% was eluted with methyl-alpha-D-glucopyranoside. Approximately 9% of the biantennary complex oligosaccharides on SHBG of control men and none of those on SHBG from alcoholic men were fucosylated on the chitobiose core, as determined by chromatography on Lenn culinaris lectin. Galactosylated oligosaccharides were also present on the SHBG fraction as indicated by its interaction with Ricinus communis-I. Approximately 24% of SHBG of alcoholic men and 39% of those on SHBG from control individuals applied to Con-A were retained and could be eluted with methyl-alpha-D-mannopyranoside. Evidence based on the binding on mannoside-eluted SHBG to Con-A, wheat germ agglutinin, and R. communis-I indicated that at least the SHBG in this fraction, from alcoholics or controls, contained two glycosylation sites and that the sites were differentially glycosylated.

Genetically polymorphic alpha-L-fucosidase (FUCA1) isozymes detected in blood plasma

The main isozyme patterns of desialylated blood plasma or serum alpha-L-fucosidase (FUCA) were found to be almost identical to those of semen, urine, placental extracts, and leukocyte lysates, when detected by polyacrylamide gel isoelectric focusing, and activity staining using the fluorogenic substrate 4-methylumbelliferyl-alpha-L-fucopyranoside. Three phenotypes (1, 2-1, and 2) determined from plasma samples were identical to the phenotypes from urine and leukocyte lysates from the same individuals. A population study of plasma samples collected from 485 Japanese individuals indicated that the frequencies of the FUCA1*1 and FUCA1*2 alleles were 0.7505 and 0.2495, respectively. The mean plasma enzyme activities (+/- SD) of the three phenotypes were 318.8 +/- 116.7 nmol/ml per h for type 1, 268.0 +/- 108.3 nmol/ml per h for type 2-1, and 233.2 +/- 84.4 nmol/ml per h for type 2. The mean activities of types 1 and 2 suggest that, on average, the FUCA1*1 gene product in plasma has about 1.4 times the activity of FUCA1*2.

Defective expression of alpha-L-fucosidase by lymphoid cells of a fucosidosis patient

Fucosidosis is an inherited lysosomal storage disease due to a deficiency of alpha-L-fucosidase activity. Exponentially growing lymphoid cell cultures from a fucosidosis patient (JH) had 16-fold lower extracellular alpha-L-fucosidase protein and 72-fold lower intracellular alpha-L-fucosidase protein with negligible catalytic activity as compared with the mean of 19 control cultures. The percentage of total alpha-L-fucosidase protein released extracellularly by JH cells was 71% as compared with 35% +/- 9% for control cells. During a 1.5 h pulse with 35S-methionine, alpha-L-fucosidase was synthesized by JH cells as an intracellular doublet with Mr of 58,000 and 56,000 and by control cells as an intracellular form with Mr = 58,000. During a subsequent 21 h chase with unlabeled methionine, JH alpha-L-fucosidase was entirely secreted. In contrast, only 25%-30% of control enzyme was secreted with the remainder retained intracellularly. Thus, JH lymphoid cells synthesized a reduced amount of alpha-L-fucosidase that was catalytically inefficient and was hypersecreted. Treatment of JH alpha-L-fucosidase with N-glycanase produced polypeptide chains with Mr of 52,000 and 54,000. Previously, treatment of control alpha-L-fucosidase with N-glycancase produced a single polypeptide chain with Mr of 52,000 (Biochem Genet 1988; 26: 401-20). The doublet polypeptide chains of alpha-L-fucosidase in JH cultures may represent expression of two distinct allelic forms of mutant alpha-L-fucosidase.

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.

The basic isoelectric form of alpha-L-fucosidase from the hepatopancreas of the shrimp Penaeus monodon (Crustacea: Decapoda)

1. alpha-L-Fucosidase was purified ca 10,889-fold to homogeneity from Penaeus monodon, with a final spec. act. of 31,250 U/mg of protein. 2. By using SDS-polyacrylamide gel electrophoresis, the monomers of shrimp alpha-L-fucosidase were discovered to have mol. wts of 63,000 and those of human placental enzyme, 46,000 and 20,000. Since the active shrimp alpha-L-fucosidase was found to have a mol. wt of 233,000 by Superose 12 FPLC, it was concluded that the purified shrimp enzyme was tetrameric. 3. In contrast to the discovery of thermolability with human placental alpha-L-fucosidase, the shrimp enzyme was found to be stable to heating at 65 degrees C for 10 min. 4. The shrimp alpha-L-fucosidase has an isoelectric point (pI) of 8.5, but the human placental enzyme has a pI of 4.0. The shrimp enzyme was sialyated. 5. The shrimp alpha-L-fucosidase has a pH optimum at 5.5 and its Km was 22.2 microM with 4-methyl-umbelliferyl-alpha-L-fucopyranoside as substrate. The human enzyme has a broad pH optimum between 5.0 and 6.5.

Isoform, kinetic and immunochemical characterization of rodent liver alpha-L-fucosidases

alpha-L-Fucosidase from hamster and six inbred mouse strains contains two to three unique basic isoelectric forms (above pI 7.0) in addition to the usual acidic and neutral isoforms from pI 4-7. Rat liver alpha-L-fucosidase contains multiple isoforms between pI values of 4.0 and 7.3 whereas guinea pig liver alpha-L-fucosidase exhibits a single broad isoform at pI 5.3. 2. All the alpha-L-fucosidases have similar KM values (0.05-0.12 mM) for 4-methylumbelliferyl-alpha-L-fucopyranoside but pH-activity curves which are significantly different in optima and per cent of optimal activity in the acid region. 3. Double-antibody immunoprecipitation experiments indicate that rodent liver alpha-L-fucosidases crossreact to varying extents with polyclonal antibody against human liver alpha-L-fucosidase. 4. Hamster, guinea pig and mouse liver alpha-L-fucosidases exhibit significantly less binding than human and rat liver fucosidases to the agarose-epsilon-aminocaproylfucosamine affinity resin.

Antibody-affinity purification of novel alpha-L-fucosidase from mouse liver

Previous studies have documented the presence of a novel alpha-L-fucosidase in mouse liver that contains unique basic isoelectric forms and that is antigenically similar to, but not identical with, human liver alpha-L-fucosidase [Laury-Kleintop, Damjanov & Alhadeff (1985) Biochem. J. 230, 75-82]. In the present investigation, mouse liver alpha-L-fucosidase was purified approx. 26,500-fold in 10% overall yield by antibody-affinity chromatography with the IgG fraction of goat anti-(human alpha-L-fucosidase) antibody coupled to Sepharose 4B. Native polyacrylamide-gel electrophoresis and SDS/polyacrylamide-gel electrophoresis indicated that the mouse fucosidase is highly purified if not homogeneous. Isoelectric focusing demonstrated that all enzymic forms found in crude mouse liver supernatant fluids were purified by the antibody-affinity procedure.

Purification and kinetic studies of an alpha-L-fucosidase of Venus mercenaria

An alpha-L-fucosidase activity has been isolated from the liver (hepatopancreas) of the common edible clam, Venus mercenaria, and has been purified approximately 300-fold (11% yield) by affinity chromatography on agarose-epsilon-amino-caproylfucosamine. Isoelectric focusing profiles were heterogeneous, revealing several isoenzymes. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated the presence of a single subunit of Mr 50,000. The purified enzyme preparation contained only trace amounts of other alpha- and beta-D-glycosidases tested. In addition to p-nitrophenyl alpha-L-fucopyranoside, the enzyme hydrolyzed natural substrates such as fucose-containing milk pentasaccharides, thyroglobulin glycopeptides, human salivary glycoproteins, and blood-group-active glycosphingolipids. The enzyme preparation had a broad pH optimum range between 4.5 and 5.5. The apparent Km value with respect to p-nitrophenyl alpha-L-fucopyranoside was 0.26mM.

Demonstration of human alpha-L-fucosidase polymorphism by means of monoclonal antibodies

Conventional rabbit antibodies and mouse monoclonal antibodies were raised to alpha-L-fucosidase purified from human placenta. Four monoclonal antibodies were studied, of which only one (A) was able to immunoprecipitate the fucosidase activity completely. Two antibodies (B and C) precipitated 65% and one (D) 35% of the activity. The enzyme precipitated by the monoclonal antibodies remained fully active, whereas the enzyme precipitated by conventional antibodies was partly inactivated. As shown by the method of successive immunoprecipitations, the monoclonal antibodies B and C recognized the same set of placental fucosidase molecules, and D a subset thereof. The purified fucosidase also yielded two components after gel electrophoresis in nondenaturing conditions, and the slower component corresponded to the set recognized by antibodies B and C. The fucosidase extracted from different tissues and serum was studied by immunoprecipitation. In all cases, the enzyme was completely precipitated by monoclonal antibody A. Two patterns were found with B, C and D: either part of the activity was precipitated by these antibodies (leucocytes, placenta, brain, liver, spleen, thymus) or B, C and D failed to precipitate any of the enzyme (serum, heart, kidney, testes).

Purification of human liver glycoprotein sialyltransferase by affinity chromatography

A simple procedure has been developed for purifying solubilized human liver glycoprotein sialyltransferase (EC 2.4.99.1) 16000-fold in 4-5% yield. The procedure involves two centrifugation steps, affinity chromatography of the ultrasupernatant fluid on cytidine diphosphate-hexanolamine-agarose followed by gel filtration on Sephadex G-150. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) indicated that the purified sialyltransferase preparation contains approximately equivalent amounts of three protein bands (with apparent molecular weights of 61000, 63000 and 70000) and is highly purified if not homogeneous.

Porcine thyroid fucosidase

An alpha-L-fucosidase (alpha-L-fucoside fucohydrolase, EC 3.2.1.51) has been isolated from porcine thyroid tissue and purified 10,800-fold using a combination of ion exchange, affinity and molecular sieve chromatography. The enzyme appears homogeneous by SDS electrophoresis but isoelectric focusing procedures detect considerable heterogeneity. The enzyme is a glycoprotein and this fact interferes with accurate molecular weight estimates by SDS electrophoresis or molecular sieve techniques. The enzyme appears, however, to be a tetramer and density gradient measurements set its molecular weight at 192,000 +/- 3,000. The enzyme exhibits an optimum at a pH of 5.1 and shows a high order of specificity for L-fucose units linked through alpha bonds. Both sulfhydryl and carboxyl groups appear necessary for enzyme activity. The enzyme does not attack intact thyroglobulin directly but will remove fucosyl residues from the glycone moiety if the protein portion is largely removed. The enzyme thus functions in a salvage role as thyroglobulin is degraded.

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.

Properties of two forms of alpha-L-fucosidase isolated from normal human sera with low and high enzymatic activity

Studies on human alpha-L-fucosidase were performed on normal and low activity sera. After DEAE-Sephacel chromatography, two major forms of enzyme have been characterized in both types of sera. These enzymatic forms were different with respect to their thermostability and electrofocusing behaviour. The less acidic form (I) was thermolabile. In contrast, the more acidic one (II) was thermostable. But the forms I and II had respectively similar properties when isolated from either normal or low activity sera. These results suggest the presence in both types of sera of two major forms of alpha-L-fucosidase but in variable proportions. The low activity sera contained a major proportion of the thermolabile less acidic form when compared with normal activity sera.

Specificity patterns of different types of human fucosidase. Recognition of a certain region of the pyranose ring in sugars by the enzymes

Data on the hydrolysis of fucosides, galactosides and arabinosides by different types of fucosidase are presented. The comparative study of the splitting of alpha-L-fucoside and beta-D-arabinoside with a similar structure at C1--C4 of the pyranose ring and the preparation of the enzyme by affinity chromatography showed that both substrates were hydrolysed by the same enzyme, alpha-L-fucoside(beta-D-arabinoside)hydrolase. The analogous investigation of the hydrolysis of beta-D-fucoside, beta-D-galactoside and alpha-L-arabinoside with a similar structure at C1--C4 of the pyranose ring demonstrated that these glycosides were split by the same enzyne, beta-D-fucoside(beta-D-galactoside, alpha-L-arabinoside)hydrolase, the activity of which is decreased dramatically in GM1-gangliosidosis. The data obtained support the assumption that the specific action of different types of fucosidase is due to recognition by these enzymes of C1--C4 of the pyranose ring in the corresponding substrates. The problems of differential diagnosis of some glycosidoses (focosidosis, GM1-gangliosidosis and Fabry disease) are discussed on the basis of the data obtained.

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 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.

Human amniotic fluid alpha-L-fucosidase

The activity and properties of alpha-L-fucosidase in 24 samples of amniotic fluid have been investigated using the 4-methylumbelliferyl substrate. A wide range of fucosidase specific activity (0.20-1.45 nmol/min/mg protein) was found with an average value of 0.62 nmol/min/mg protein. Although no clear-cut correlation exist, there appear to be trends of decreasing fucosidase specific activity with increasing maternal age of donor and increasing gestational time. alpha-L-Fucosidase activity from four amniotic fluids was characterized kinetically and immunochemically and found not to differ in its properties due to maternal age of donor or gestational time. Isoelectric focusing revealed multiple forms between pH 5.0 and 6.8, with the majority of activity present between pH 5.0 and 6.0. The pH optimum is near pH 5.0 with a second optimum suggested at pH 6.2. The apparent Michaelis constant (Km) for the 4-methylumbelliferyl substrate is 0.05 +/- 0.01 mM. The enzyme is completely thermostable at 37 degrees C for at least 4 h but loses 95% of its activity after preincubation at 45 degrees C for 1 h. Double immunodiffusion and immunoprecipitation experiments using anti-liver alpha-L-fucosidase antibody suggest that the amniotic fluid alpha-L-fucosidase is antigenically similar, if not identical, to the human liver enzyme.

Purification and characterisation of alpha-L-fucosidase from human placenta. pH-dependent changes in molecular size

alpha-L-Fucosidase has been purified 12 000 fold from human placenta. The enzyme is a glycoprotein containing, by weight: 0.9% galactose; 1.9% mannose, 1.9% N-acetylglucosamine and 1.9% N-acetylneuraminic acid. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate separated proteins with molecular weights ot 55 000, 51 400 and 25 000. Resolution of the two larger protein bands varied with the gel system and these proteins may differ only in carbohydrate content. Gel filtration of te purified enzyme failed to separate the three proteins. Treatments with the cross-linking reagent dimethyl suberimidate prior to electrophoresis, resulted in a diminution of the original protein bands and the formation of oligomers with molecular weights of 80 000, 100 000, 130 000, and 144 000. These results suggest that the heavy (55 000 and 51 400) and light (25 000) proteins are structurally associated. The molecular weight of the native enzyme, measured by gel filtration, was dependent on the pH of the eluting buffer. At pH 5.0 or 6.0 a catalytically active peak was observed, with a molecular weight of 305 000. At pH 7.5 this peak was completely absent and the enzyme eluted as an asymmetrical peak with an apparent molecular weight of about 60 000. The reduction in apparent molecular weight at pH 7.5 was reversible by dialysis of isolated fractions at pH 6.0. In agreement with these findings the sedimentation coefficient was 8.5 S at pH 5.0 but only 3.6 S at pH 7.5. The results can be accounted for by the existence of a pH-dependent equilibrium between aggregated and dissociated forms of the enzyme or by pH-depedent conformational changes.

Subunit composition of human liver alpha-L-fucosidase

The subunit composition of human liver alpha-L-fucosidase was studied by using three different procedures for treating and electrophoresing the purified enzyme. Although the presence on only one subunit was found by conventional procedures using sodium dodecyl sulphate and urea, two non-identical subunits with mol. wts. of 59 000 and 54 000 were found when the alpha-L-fucosidase was reduced and S-carboxymethylated with iodoacetate followed by electrophoresis on polyacrylamide gels containing 0.1% sodium dodecyl sulphate and 8.0 M-urea.