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

Cellular prion protein dysfunction in a prototypical inherited metabolic myopathy

Inherited fatty acid oxidation diseases in their mild forms often present as metabolic myopathies. Carnitine Palmitoyl Transferase 2 (CPT2) deficiency, one such prototypical disorder is associated with compromised myotube differentiation. Here, we show that CPT2-deficient myotubes exhibit defects in focal adhesions and redox balance, exemplified by increased SOD2 expression. We document unprecedented alterations in the cellular prion protein PrPC, which directly arise from the failure in CPT2 enzymatic activity. We also demonstrate that the loss of PrPC function in normal myotubes recapitulates the defects in focal adhesion, redox balance and differentiation hallmarks monitored in CPT2-deficient cells. These results are further corroborated by studies performed in muscles from Prnp-/- mice. Altogether, our results unveil a molecular scenario, whereby PrPC dysfunction governed by faulty CPT2 activity may drive aberrant focal adhesion turnover and hinder proper myotube differentiation. Our study adds a novel facet to the involvement of PrPC in diverse physiopathological situations.

Classification of IVS1-10T-->C as a polymorphism of BRCA1

Mutations inactivating the tumor suppressor gene BRCA1 may be responsible for disease for up to 80% of familial ovarian cancer cases. In this syndrome, tumorigenesis classically initiates from an inherited mutation in one allele followed by somatic deletion of the normal allele. Sequencing of BRCA1 amplified from genomic DNA of lymphocytes and microdissected ovarian tumor cells of a familial ovarian cancer patient revealed three, rare heterozygous DNA variations (2418delA, 233G-->A, and IVS1-10T-->C) in both tumor and constitutional (lymphocyte) DNA. Thus, both copies of BRCA1 were retained in tumor. Haplotype analysis of the patient and four siblings assigned 2418delA to one copy of BRCA1 and 233G-->A and IVS1-10T-->C to the other. The DNA change, 2418delA, is considered a mutation that inactivated one BRCA1 allele because it caused a frameshift and generation of a premature stop codon, resulting in synthesis of a truncated peptide as evidenced by an in vitro protein truncation test. The DNA variation, 233G-->A, does not result in an amino acid change, and is considered a benign polymorphism. IVS1-10T-->C is a unique BRCA1 change that occurs in the last nucleotide of a consensus sequence for a branch site critical for RNA splicing. Therefore, we investigated whether IVS1-10T-->C deleteriously affected BRCA1 splicing or expression, and thereby inactivated the other BRCA1 allele. Using the technique of reverse transcription-polymerase chain reaction (PCR) with RNA isolated from lymphoid cell lines of the patient and of controls, no evidence was found that IVS1-10TC abnormally disrupted mRNA splicing or caused the absence of BRCA1 mRNA. Thus, IVS1-10T-->C is not harmful to BRCA1 function, and is classified a benign polymorphism. Retention of the normal BRCA1 allele in the tumor with the heterozygous germline BRCA1 mutation, 2418delA, indicated that mutational inactivation of both BRCA1 alleles was not required for tumorigenesis. It is possible that the normal allele may be functionally inactivated by a nonmutational mechanism.

Mutation analysis of BRCA1, TP53, and KRAS2 in ovarian and related pelvic tumors

Cancer may be viewed as a genetic disease resulting from critical mutations that disrupt normal cell growth. To characterize the involvement of the BRCA1 and TP53 tumor suppressor genes and of the KRAS2 protooncogene in gynecologic cancer, mutation analysis of these genes was conducted in pelvic tumors of 85 patients that included 49 epithelial ovarian carcinoma cases. The 85 pelvic tumors contained 5 tumors with BRCA1 mutations, 33 with TP53 mutations, and 1 with a KRAS2 mutation. Each of the BRCA1 and KRAS2 mutations, and 25 of the TP53 mutations, were in ovarian carcinomas. Four of the BRCA1 mutations were germline and 1 was somatic. The 4 patients with germline BRCA1 mutations had an early age of disease onset (33-48 years) relative to the mean age of onset (58 years) of all 49 ovarian carcinoma patients, and 3 of these 4 patients had a family history of ovarian or breast cancer. None of the 4 tumors with germline BRCA1 mutations had a KRAS2 mutation or a TP53 mutation, despite a 51% frequency of TP53 mutations in the 49 ovarian carcinomas. Three of the 4 tumors with germline BRCA1 mutations retained a wild-type BRCA1 allele. The tumor with the somatic BRCA1 mutation contained a TP53 mutation and had no evidence for wild-type BRCA1 and TP53 alleles. These data suggest that both BRCA1 and TP53 were inactivated in 1 of 49 ovarian carcinomas. Moreover, mutational inactivation of both BRCA1 and TP53 did not occur in 4 tumors with a germline BRCA1 mutation. It has been proposed that tumorigenesis in cells with a heterozygous BRCA1 mutation requires inactivation of the wild-type BRCA1 and TP53 alleles, which results in genomic instability and acquisition of mutations in protooncogenes. Clearly, mutational inactivation of TP53 and the wild-type BRCA1 allele in ovarian tumors with a heterozygous, germline BRCA1 mutation is not an absolute requirement for tumor formation. It is possible that these alleles may be inactivated by nonmutational mechanisms or that other tumor formation pathways exist.

Correlation of TP53 mutations and p53 expression in ovarian tumors

To characterize the involvement of the TP53 tumor suppressor gene in ovarian cancer, mutation analysis of exons 2-11 of TP53 and immunodetection of its protein product, p53, were done in 48 ovarian tumors. Normally, p53 is not immunodetectable. Missense TP53 mutations have been reported to result in p53 accumulation and detection, but mutations generating premature stop codons have not. Mutations were identified in 19 of 41 malignant tumors but not in 5 benign tumors and 2 tumors of low malignant potential. Fifteen of the 19 tumors with mutations also stained positively by immunohistochemistry or Western blot or both. They included 11 missense mutations, 1 in-frame duplication (474ins6), and 3 frameshift mutations generating premature stop codons. The three tumors with frameshifts also had a wild-type TP53 allele and displayed normal size but not truncated p53 by Western blot. This indicates that these tumors express wild-type p53. The significance of TP53 mutations in the development of the three tumors is questionable unless there is a mechanism for inactivating wild-type p53. Nine of the 19 mutations found here, including the 3 frameshifts, were previously not reported in ovarian cancer. Thirteen of the 19 mutations were single nucleotide substitutions with 6 transitions and 7 transversions. The ratio of transversions to transitions (1.2) was different from literature reports (0.5) (P < 0.01). Thus, the spectrum of TP53 mutations in our study differed from other ovarian tumor reports. This difference may be due to population-based differences in the molecular epidemiology of TP53 mutations.

Isolation of a melibiose-binding protein from human spleen

A melibiose-binding protein was isolated from human spleen by serial affinity chromatography on lactose-, mannose-, and melibiose-Sepharose. The purified protein agglutinated rabbit erythrocytes and re-bound to melibiose, but did not bind to murine nor human laminin. The protein was composed of approximately 58 kDa and 26 kDa polypeptides. The polypeptides were detected in buffy coat cell extracts and they were synthesized in vitro by B lymphoblastoid cells. The polypeptides did not react with anti-galaptin, anti-C-reactive protein, anti-amyloid P, anti-keratin, and anti-rat lung lectin 29 sera. The 58 kDa polypeptide reacted very weakly with anti-core-specific lectin serum and reacted with anti-IgG serum. The data suggest that the major protein isolated is an anti-Ga1 alpha 1-->6 immunoglobulin.

Pedigree analysis of alpha-L-fucosidase gene mutations in a fucosidosis family

Fucosidosis is an autosomal recessive lysosomal storage disease resulting from absence of alpha-L-fucosidase activity. Lymphoid cell lines from two siblings with fucosidosis and a healthy individual (control) had alpha-L-fucosidase mRNA of normal size (2.3 kb) but the level of alpha-L-fucosidase mRNA in the patients' cells was reduced. cDNA was prepared and amplified from alpha-L-fucosidase mRNA of lymphoid cells of the patients, their carrier parents, and the control. Direct DNA sequencing demonstrated three mutations in the fucosidosis family. One mutation, C1282-->T, changed the codon (CAA) for Gln-422 to a stop codon (UAA). This mutation was heterozygous (C and T) in the patients and their father and independently confirms an earlier report (J. Mol. Neurosci. (1989) 1, 177). Another mutation, C247-->T, changed the codon (CAG) for Gln-77 to a stop codon (UAG) and was heterozygous (C and T) in the patients and their mother. The third mutation, A860-->G, changed the codon CAG for Gln-281 to the codon (CGG) for Arg and was heterozygous (A and G) in the patients but homozygous in their father. alpha-L-Fucosidase activity in cells of the father was 37% of controls indicating that homozygosity of the A860-->G mutation did not cause an absence of alpha-L-fucosidase activity and fucosidosis. This mutation probably results in a normal polymorphic variant of alpha-L-fucosidase. It is proposed that the combination of the C247-->T mutation on the maternal allele of the alpha-L-fucosidase gene and the C1282-->T mutation on the paternal allele caused fucosidosis in the patients.

A mutation generating a stop codon in the alpha-L-fucosidase gene of a fucosidosis patient

Fucosidosis is an autosomal recessive, lysosomal storage disease featured by deficient activity of alpha-L-fucosidase. Lymphoid cell lines from a fucosidosis patient (JT) and a healthy individual (control) contained alpha-L-fucosidase mRNA of the same size, 2.3 Kb, as determined by Northern blot analysis. cDNA was prepared from alpha-L-fucosidase mRNA of JT and control cells and each cDNA was amplified by the polymerase chain reaction. Direct DNA sequencing of the amplified products revealed a single mutation in JT, a G1141-->T transition. This changed the codon (GAA) for Glu-375 to a stop codon (UAA). Amplification and sequencing of the area containing the G1141-->T transition in genomic DNA of JT and control cells demonstrated that the mutation was homozygous in JT. Analysis of cDNA and genomic DNA derived from lymphoid cells of mother JT revealed her to be heterozygous (G and T) at position 1141. The G1141-->T mutation is probably responsible for disease in JT.

Lymphoblastoid cell adhesion mediated by a dimeric and polymeric endogenous beta-galactoside-binding lectin (galaptin)

Glutaraldehyde-polymerized human splenic galaptin, a beta-galactoside-binding lectin, was demonstrated to have enhanced hemagglutinating and asialofetuin binding activity relative to native dimeric galaptin when these lectins were present in solution. The polymerized lectin consisted primarily of 2-, 4- and 12-membered species after reductive alkylation. Both forms of galaptin bound, at 4 degrees C, to saturable B lymphoblastoid cell surface receptors. Estimates obtained by Scatchard analyses, with the binding data expressed in terms of 14.5 kDa subunit molarity, were 5 x 10(7) binding sites/cell with affinity constant Ka = 2.2 x 10(5) M for dimeric galaptin and 17 x 10(7) binding sites/cell with Ka = 3.4 x 10(5) M-1 for polymeric galaptin. Both forms of galaptin adsorbed to polystyrene with high efficiency; however, only plastic-adsorbed polymeric galaptin mediated adhesion of lymphoblastoid cells. Cell adhesion was inhibited by lactose. Plastic-adsorbed polymeric galaptin bound asialofetuin more efficiently than dimeric galaptin. Asialofetuin binding was inhibited 65% and 30-50% by lactose for plastic-adsorbed polymeric and dimeric galaptin, respectively. Native fetuin bound to the adsorbed dimeric galaptin in a lactose-insensitive manner. These data indicate that cell surface receptor-galaptin interaction is carbohydrate specific whereas polystyrene-adsorbed galaptin may demonstrate protein-protein interactions with soluble ligands.

Binding receptors for alpha-L-fucosidase in human B-lymphoid cell lines

An established mechanism for directing newly made acid hydrolases to lysosomes involves acquisition of mannose 6-phosphate residues by the carbohydrate portion of acid hydrolases followed by binding to specific membrane-bound transport receptors and delivery to lysosomes. Two distinct phosphomannosyl receptors (CI-MPR and CD-MPR) have been identified. Alternative mechanisms for trafficking acid hydrolases exist. This report examines means for the possible receptor-mediated intracellular transport of alpha-L- fucosidase in lymphoid cells. The binding of alpha-L-fucosidase to intact cells and to total cell membrane preparations, in conjunction with immunoassays of solubilized membrane preparations, revealed the presence of CI-MPR and CD-MPR on human lymphoid and fibroblast cell lines. The mean level of CD-MPR in nine lymphoid cell lines was 7.2-fold greater than CI-MPR. The mean level of CI-MPR in two fibroblast lines was 3.8-fold greater than CD-MPR. The mean content of CI-MPR was 19.5-fold greater in the fibroblasts than in the lymphoid cells. The CD-MPR content of fibroblasts and lymphoid cells was nearly equivalent. Among these cell lines were a fibroblast and a lymphoid line from the same individual. These results indicate that human B-lymphoid cells are deficient in CI-MPR and suggest that modulation of expression of CI-MPR and CD-MPR in lymphoid cells differs from that in fibroblasts, including cell lines with identical genomes. No specific receptor capable of binding alpha-L-fucosidase independent of mannose 6-phosphate was demonstrable, despite published results that support the existence of a mannose 6-phosphate independent trafficking mechanism in lymphoid cells for this enzyme.

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.

Synthesis and processing of lysosomal alpha-fucosidase in cultured human fibroblasts

The lysosomal enzyme alpha-L-fucosidase from human skin fibroblasts is synthesized as a 53 kDa glycosylated precursor which is then proteolytically processed to a 50 kDa mature form. This was confirmed by pulse-chase labeling studies with chase times up to 72 h. In fibroblasts treated with 1-deoxymannojirimycin to prevent trimming of high mannose oligosaccharides, endoglycosidase H (endo H) treatment completely deglycosylated and reduced the size of immunoprecipitated alpha-fucosidase by 4-5 kDa, suggesting the presence of two oligosaccharide units. Endoglycosidase H and endo F studies on untreated alpha-fucosidase suggested the presence of one complex-type and one high mannose-type unit, and that the final processing from 53 to 50 kDa did not involve the removal of carbohydrate. Processing was inhibited by the thiol proteinase inhibitor Ep-459, but not by Ep-475 or leupeptin. Since Ep-459 treatment increased both alpha-fucosidase activity (3-fold) and the amount of immunoprecipitable alpha-fucosidase protein in normal human skin fibroblasts, this suggests a role for cysteine-like proteinases either directly or indirectly in lysosomal hydrolase processing and turnover. Subcellular fractionation studies revealed that the proteolytic processing of the 53 kDa precursor to the 50 kDa mature form occurred in the lysosome, or some other dense organelle.

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.

Fucosidosis revisited: a review of 77 patients

Fucosidosis is a rare, autosomal recessive, lysosomal storage disorder caused by a severe deficiency of alpha-L-fucosidase in all tissues. We have conducted a review of fucosidosis, compiling data from published reports and an international questionnaire survey. Seventy-seven patients affected with fucosidosis of which 19 had not been reported before have been identified. A major aim of the present study was to define the natural history of fucosidosis. The clinical picture of fucosidosis consists of progressive mental (95%) and motor (87%) deterioration, coarse facies (79%), growth retardation (78%), recurrent infections (78%), dysostosis multiplex (58%), angiokeratoma corporis diffusum (52%), visceromegaly (44%), and seizures (38%). Whereas the original fucosidosis patients described by Durand et al. (J. Pediatr 75:665-674, 1969) were decerebrate and died before age 5 years, most fucosidosis patients have a slower course of degeneration. Mortality before age 5 years was observed in only 7 patients (9%), whereas 36 patients (64%) reached the second decade. We did not find evidence for the existence of clinical heterogeneity with a rapidly progressive type I and a slowly progressive type II fucosidosis as suggested in the literature. Instead, there seems to exist a wide continuous clinical spectrum. At the biochemical level no heterogeneity in residual fucosidase enzyme activity or cross-reacting immunoreactive fucosidase protein was observed. At the DNA level at least 4 different mutations must be responsible for fucosidosis. These genotypic differences however do not explain the observed phenotypic differences.

Metabolic correction of fucosidosis lymphoid cells by galaptin-alpha-L-fucosidase conjugates

To determine if isolated galaptin, an endogenous galactoside-binding lectin, could serve as a transport vehicle of therapeutic agents to cells, galaptin and alpha-L-fucosidase were coupled using glutaraldehyde. The conjugates were incubated with alpha-L-fucosidase-deficient, EBV-immortalized lymphoid cells from a fucosidosis patient. Conjugates were effectively bound and internalized by the cells in a lactose inhibitable manner. Internalization of conjugate resulted in the reduced accumulation of alpha-L-fucosyl-N-acetylglucosaminylasparagine, a glycopeptide that accumulates in cells of fucosidosis patients, to levels found in lymphoid cells from a healthy individual. Thus, galaptin-alpha-L-fucosidase conjugates may be useful for enzyme replacement therapy of fucosidosis. The concept of using galaptin as a transport vehicle may be applied to the delivery of other compounds to cells bearing galaptin receptors.

Role of galaptin in ovarian carcinoma adhesion to extracellular matrix in vitro

Immunohistochemical studies indicated that galaptin is a major protein of ovarian carcinoma cells present in patient effusions and it is distributed throughout the cytoplasm. Enzyme-linked immunoadsorbent assay (ELISA) and immunoprecipitation experiments demonstrated that galaptin is also a major protein of the A121 ovarian carcinoma cell line, constituting less than or equal to 1% of extractable protein bound by DEAE Sephacel. Western blot analyses revealed that the galaptin present in ovarian carcinoma consists of a 14.5 KD subunit. Ovarian carcinoma and mesothelial cells isolated from patient effusions display surface receptors for galaptin with an apparently greater density of receptors present on the carcinoma cells. A121 cells also display surface receptors for galaptin: binding sites/cell = 3 X 10(8) and Ka = 1.2 X 10(9) M-1. The presence of galaptin in bovine corneal endothelial cells (BCEC) and BCEC-derived extracellular matrix (ECM) was demonstrated by ELISA. Of the total ECM-bound galaptin, about 75% appears to be insoluble in phosphate-buffered saline (PBS) lactose. ECM was also found to contain abudnant receptors for galaptin. Treatment of ECM with lactose increased the apparent galaptin receptor density:binding sites/cm2 = 7 X 10(13) and Ka = 2.6 X 10(9) M-1. Pretreatment of A121 cells with galaptin inhibited adhesion to ECM. The addition of exogenous galaptin to ECM had variable effect on cell adhesion. The data presented here suggest that early adhesion events may be carbohydrate-specific involving interaction between ECM-bound galaptin and cell surface galaptin receptors.

Effect of glycosylation inhibitors and acidotropic amines on the synthesis, processing, and intracellular-extracellular distribution of alpha-L-fucosidase in B-lymphoblastoid cells

N-Methyldeoxynojirimycin, 1-deoxymannojirimycin, and monensin interferred with normal processing of asparagine-linked oligosaccharide chains of alpha-L-fucosidase in lymphoid cells by blocking conversion of high-mannose oligosaccharides of newly made precursor enzyme to complex oligosaccharides of mature intracellular and extracellular forms of enzyme. These compounds did not substantially alter the distribution of newly made alpha-L-fucosidase between intracellular and extracellular compartments. Thus, sorting of newly made alpha-L-fucosidase molecules that are retained intracellularly from molecules that are eventually secreted does not require terminal glycosylation or the trimming of glucose or alpha-D-(1----2)-linked mannose residues from carbohydrate chains. Chloroquine and ammonium chloride had no substantial effect on the structural processing or on the intracellular-extracellular distribution of alpha-L-fucosidase in lymphoid cells. In other cell types, these weak bases caused a massive secretion and an intracellular deficiency of acid hydrolases. The different responses to weak bases in lymphoid cells and the other cell types can be explained either by an inability of these agents to neutralize the pH of intracellular organelles in lymphoid cells or by a routing mechanism in lymphoid cells that is independent of pH.

Isolation and sequence analysis of a cDNA encoding rat liver alpha-L-fucosidase

cDNA clones for alpha-L-fucosidase were isolated from a rat liver lambda gt11 expression library by using both monospecific polyclonal antibodies against the affinity-purified enzyme and biotinylated rat liver fucosidase cDNA sequences as probes. The largest clone, lambda FC9, contained a 1522 bp full-length cDNA insert (FC9) that encoded the 434-amino acid-residue subunit (Mr 50439) of rat liver alpha-L-fucosidase. A putative signal peptide 28 amino acid residues in length preceded the sequence for the mature protein. In addition, FC9 specified for 11 nucleotide residues of 5' untranslated sequence, 78 nucleotide residues of 3' untranslated sequence and a poly(A) tail. The deduced amino acid sequence from FC9 in conjunction with the experimentally determined N-terminus of the mature enzyme suggested that rat liver fucosidase did not contain a pro-segment. However, there was the possibility of limited N-terminal processing (one to five amino acid residues) having occurred after removal of the predicted signal peptide. Amino acid sequences deduced from FC9 were co-linear with amino acid sequences measured at the N-terminus of purified fucosidase and on two of its CNBr-cleavage peptides. An unusual aspect of rat liver alpha-L-fucosidase protein structure obtained from the FC9 data was its high content of tryptophan (6%). The coding sequence from FC9 showed 82% sequence identity with that from a previously reported incomplete human fucosidase sequence [O'Brien, Willems, Fukushima, de Wet, Darby, DiCioccio, Fowler & Shows, (1987) Enzyme 38, 45-53].

Abnormal expression of alpha-L-fucosidase in lymphoid cell lines of fucosidosis patients

Fucosidosis is an autosomal recessive lysosomal storage disease due to a deficiency of alpha-L-fucosidase activity in tissues and body fluids. Exponentially growing lymphoid cell cultures from four fucosidosis patients had 2.7-fold to 15.6-fold less extracellular alpha-L-fucosidase protein and 28.8-fold to 144.0-fold less intracellular alpha-L-fucosidase protein with negligible catalytic activity, compared to the mean of 19 control cultures. The percentage of total alpha-L-fucosidase protein released extracellularly by cultures from the four patients was 64 to 85%, compared to 35 +/- 9% for control cultures. Intracellular and extracellular enzyme forms in fucosidosis and control cell lines were glycoproteins containing polypeptide chains of Mr = 52,000. During a 1.5-hr pulse-label with 35S-methionine, alpha-L-fucosidase was synthesized by control cells and two fucosidosis cell lines as an intracellular form with Mr = 58,000. During a subsequent 21-hr chase with unlabeled methionine, mutant enzyme was almost entirely processed to an extracellular form with Mr = 62,000. In contrast, only 25-30% of control enzyme was processed to an extracellular form (Mr = 62,000), with the remainder retained intracellularly (Mr = 60,000). In the other two fucosidosis cell lines, alpha-L-fucosidase was synthesized as an intracellular form with Mr = 56,000 that was processed to an extracellular form with Mr = 60,000. In summary, the fucosidosis mutation(s) affected the catalytic activity, quantity, and extracellular release of alpha-L-fucosidase as expressed by lymphoid cells.