Pseudo arylsulfatase a deficiency: Evidence for a structurally altered enzyme

Analysis of arylsulfatase A from pseudo arylsulfatase A deficiency fibroblasts by sodium dodecyl sulfate polyacrylamide gel electrophoresis and immunoradiochemical nitrocellulose blot radiography revealed two subunit bands which migrated faster than subunit bands of enzyme from normal fibroblasts. Immunoreactive material was present only at levels comparable to enzyme activity. These findings imply that arylsulfatase A in pseudodeficiency is structurally altered, but it is catalytically equivalent to normal arylsulfatase A. This altered enzyme must be the product of the pseudodeficiency gene since no immunoreactive product of the metachromatic leukodystrophy gene could be detected in metachromatic leukodystrophy cells by the procedure employed. It is not clear from the present data if the attenuated arylsulfatase A activity in pseudodeficiency results from a decreased rate of synthesis or an increased lability of the mutant enzyme.     

Synthesis and maturation of cross-reactive glycoprotein in fibroblasts deficient in arylsulfatase a activity

The biosynthesis of arylsulfatase A was studied in cultured fibroblasts by pulse-chase labeling with [2-³H]mannose; the enzyme was isolated by immunoprecipitation and denaturing polyacrylamide gel electrophoresis. In normal fibroblasts, and in fibroblasts from a patient with multiple sulfatase deficiency, the enzyme was synthesized as a glycoprotein of apparent molecular weight of 59,000; half of it was processed over a period of 4 days to M_r= 57,000. The precursor chain of M_r= 59,000 was secreted in the presence of 10 mM NH₄Cl. An immunoprecipitable glycoprotein of normal size was synthesized by fibroblasts from two unrelated patients with metachromatic leukodystrophy, but this material disappeared within twenty hours. In fibroblasts from an individual with pseudodeficiency of arylsulfatase A, the immunoprecipitable precursor glycoprotein was smaller (M_r= 56,000). The synthesis of cross-reactive proteins with altered properties supports the concept of allelic mutations as the genetic basis of metachromatic leukodystrophy and of arylsulfatase A pseudodeficiency.     

Synthesis and stability of arylsulfatase A and B in fibroblasts from multiple sulfatase deficiency

Fibroblasts from patients with multiple sulfatase deficiency were analyzed for activities of arylsulfatase A and B, iduronate 2-sulfatase and sulfamatase. A group of patients (group I) severely deficient in all sulfatases (residual activities less than or equal to 10% of control) were differentiated from patients (group II) with residual sulfatase activities of up to 90% of control. The synthesis and stability of arylsulfatase A and B were determined in pulse-chase labelling experiments. The apparent rate of synthesis of arylsulfatase A and B varied from 30% to normal in both fibroblasts from group I and II multiple sulfatase deficiency. In group I the molecular activity of the arylsulfatase A and B was more than 10-fold lower than in control fibroblasts. In group II the molecular activity of the arylsulfatase A was twofold to threefold lower and that of arylsulfatase B half of normal. In fibroblasts of both groups the stability of arylsulfatase A polypeptides was significantly diminished. For arylsulfatase B the instability was restricted to the mature 47000-Mr polypeptide and was variable within both groups. These results demonstrate that multiple sulfatase deficiency is a heterogeneous disorder, in which the primary defects can impair both the catalytic properties and the stability of sulfatases.     

Studies on the charge isomers of arylsulfatase A

Human liver arylsulfatase A was resolved into six fractions by narrow pH range preparative isoelectric focusing. Analytical isoelectric focusing revealed that most enzyme fractions were composed of two adjacent charge isomers. Nevertheless, there was considerable enrichment of charge species which allowed a comparative study of selected properties. Except for the most cationic fraction, neuraminidase treatment converted enzyme in all fractions to the three most cationic species. The most electronegative enzyme species had the highest molecular mass being made up of 64-kDa subunits. As electronegativity decreased, there was concomitant decrease in molecular mass and increase in complexity of subunit composition. Two subunits--61 and 55 kDa--prevailed with increasing proportions of the smaller unit with loss of electronegativity. There was also an increasing amount of a 26-kDa fraction which became a substantial component of the most cationic subfraction. Only enzyme in the two fractions containing the largest and most anionic species were taken up by cultured fibroblasts at higher efficiency than unfractionated enzyme. It is suggested that processing or maturation of arylsulfatase A incurs stepwise removal of charge groups and/or peptide segments leading to smaller, less-charged enzyme species.     

Multiple sulfatase deficiency: degradation of arylsulfatase A and B after endocytosis in fibroblasts

Multiple sulfatase deficiency can be classified into group I with severe and group II with moderate deficiencies in sulfatases. In fibroblasts in both groups the stability of arylsulfatase A and of the 47000-Mr form of arylsulfatase B is decreased [F. Steckel, A. Hasilik & K. von Figura (1985) Eur. J. Biochem. 151, 141-145]. After endocytosis in control fibroblasts or those from multiple sulfatase deficiency, arylsulfatase A and B derived from the latter were subjected to enhanced degradation in both types of recipient cells. The degradation was closely linked in time to endocytosis. Whereas instability of arylsulfatase A derived from different cell lines from multiple sulfatase deficiency was comparable, a marked heterogeneity was observed for the instability of the 47000-Mr polypeptide of arylsulfatase B. Each of the cell lines from multiple sulfatase deficiency synthesized arylsulfatase A and B polypeptides with normal and with decreased stability. Treatment with benzyloxycarbonyl-Phe-Ala-CHN2, an inhibitor of cysteine proteinases, stabilized arylsulfatase A polypeptides and partially restored arylsulfatase A activity in group II fibroblasts. The inhibitor had no protective effect on the 47000-Mr polypeptide or the activity of arylsulfatase B. The bearing of these findings on the yet unknown primary defect in multiple sulfatase deficiency is discussed.     

Presence of arylsulfatase A (ARS A) in multiple sulfatase deficiency disorder fibroblasts.

Multiple deficiency disorder fibroblasts cultured in MEM-CO2 showed deficiencies of arylsulfatase A(ARS A) comparable to the deficiency in metachromatic leukodystrophy fibroblasts. However, the MSDD fibroblasts cultured in MEM-HEPES contained near normal levels of ARS A. Moreover, the enzyme from the latter fibroblasts was indistinguishable from ARS A of control fibroblasts on DEAE-cellulose chromatography, ratio of activity with several substrates, thermal inactivation, sensitivity to inhibitors, and precipitation by antiserum to human ARS A. These data support the conclusion that the ARS A genome is intact in MSDD fibroblasts and, by extension, in MSDD patients. Other sulfatases were present at levels ranging from mildly deficient to near normal but never as low as seen in the corresponding specific sulfatase deficient disorders.     

Placental steroid deficiency: association with arylsulfatase A deficiency

A family with an obstetric history consistent with placental sulfatase deficiency has X-linked ichthyosis. Steroid sulfatase deficiency was confirmed in placenta, leukocytes, and cultured skin fibroblasts of affected males; arylsulfatase A diminution was also observed in these tissues of both affected males and 2 generations of related females. No symptoms of metachromatic leukodystrophy are present in any family members. In this family, placental sulfatase deficiency, and arylsulfatase A pseudodeficiency are nonallelic.     

Structural and immunochemical characterization of human urine arylsulfatase A purified by affinity chromatography

Arylsulfatase A (aryl-sulfate sulfohydrolase, EC 3.1.6.1) was isolated from an ammonium sulfate precipitate of urinary proteins using two different affinity chromatography methods. One method involved the use of concanavalin A-Sepharose affinity chromatography at an early stage of purification, followed by preparative polyacrylamide gel electrophoresis. The other procedure employed arylsulfatase subunit affinity chromatography as the main step and resulted in a remarkably efficient purification. The enzyme had a specific activity of 63 U/mg. The final preparation of arylsulfatase A was homogeneous on the basis of polyacrylamide gel electrophoresis at pH 7.5, and by immunochemical analysis. However, when an enzyme sample obtained by either method of purification was subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis under reducing or non-reducing conditions, peptide subunits, of 63.5 and 54.5 kDa, were observed. Immunological tests with 125I-labeled enzyme established the presence of a common protein component in both of the electrophoretically separable peptide subunits of human urine arylsulfatase. The amino acid analysis of homogeneous human urine arylsulfatase A showed only a few differences between it and the human liver enzyme. However, immunological cross-reactivity studies using rabbit anti-human urine arylsulfatase revealed immunological difference between the human urine and liver arylsulfatase A enzymes.     

Characterization of human arylsulfatase a glycans

Despite numerous studies on arylsulfatase A, the structure of the glycans present in each of its two subunits has not been determined. This is important because the carbohydrate component of human arylsulfatase A synthesized in tumor tissues and transformed cells has been shown to undergo apparent changes. This study elucidates some of their major features.Glycan chain analysis of native and deglycosylated arylsulfatase A as well as its subunits was performed with the use of a Glycan Differentiation Kit and lectin affinity chromatography. Each of the two subunits of arylsulfatase A from placenta, separated electrophoretically on polyacrylamide gel in reducing conditions, reacted with digoxigenin-labelled Galantus nivalis agglutinin and Aleuria awantia agglutinin, while those from liver enzyme reacted with the former only. The subunits of both enzymes did not react with Sambucus nigra, Maakia amuriensis, Datura stramonium or Peanut agglutinin. Deglycosylation of arylsulfatase A with peptide N-glycosidase F and endo-β-N-acetylglucosaminidase F resulted in complete cleavage of its carbohydrate component from each subunit. Their molecular weights decreased by 3 kDa. Neuraminidase treatment of the enzyme from liver and placenta followed by isoelectrofocusing separation showed the presence of sialylated forms which constituted a small percentage of total enzyme activity. Placental arylsulfatase A became bound to Lens culinaris agglutinin agarose, while no interaction with Ricinus communis or Griffonia simplicifolia agglutinin agarose was observed.The study shows that both subunits of arylsulfatase A from human placenta possess two high mannose/hybrid type glycans as major structures, with at least one 6-O-l-fucose bound to the innermost N-acetylglucosamine on each. The enzyme from liver does not possess fucose. Complex type glycans containing sialic acid constitute a small percentage of the total carbohydrate component.     

Targeting of phosphomannosyl-deficient arylsulfatase A to lysosomes of I-cell fibroblasts

Fibroblasts from I-cell disease, a genetically-determined lysosomal storage disease, are shown to contain large amounts of phase-dense lysosomes. These lysosomes accumulated acridine orange and were specifically labeled with antibodies to arylsulfatase A. In normal skin fibroblasts the number of arylsulfatase-containing lysosomes was considerably lower. By immunocytochemistry, metabolic labeling and enzyme assay, the arylsulfatase A in I-cell fibroblasts was shown to be synthesized, stored and secreted at a level that was several-fold higher than that present in heterozygous I-cell or normal fibroblasts. Arylsulfatase A in I-cell fibroblasts differed from arylsulfatase in normal fibroblasts by the absence of endoglycosidase H-sensitive phosphorylated oligosaccharides. These findings indicate that arylsulfatase A in I-cells is targeted to lysosomes by a mechanism that does not appear to involve the phosphorylated mannose marker.     

Evidence for the presence of a very high concentration of arylsulfatase A in the pig thyroid: identification of arylsulfatase A subunits as the two major glycoproteins in purified thyroid lysosomes

In addition to their general function in cellular homeostasis, thyroid lysosomes play an essential role in the biosynthesis of thyroid hormones by cleaving the macromolecular prohormone, thyroglobulin. In the present work, we have attempted to determine whether the enzyme composition of thyroid lysosomes differs from that of lysosomes from other tissues. Lysosomal enzymes, cathepsin D, beta-D-galactosidase, beta-D-glucosidase, alpha-D-mannosidase, alpha-L-fucosidase, hexosaminidase, and arylsulfatase A and B, were assayed in crude fractions from various pig tissues, heart, brain, liver, kidney, thyroid, adrenals, ovary, and spleen. It appeared that the specific activity of arylsulfatase A was at least 20 times higher in the thyroid than in most other tissues. Thyroid lysosomes purified by isopycnic centrifugation on Percoll gradients contained two major polypeptides with apparent molecular weights of 58,000 and 54,000 representing about 30% of the total protein. These polypeptides were glycosylated and were exclusively found in the intralysosomal soluble fraction obtained by osmotic pressure-dependent lysis. By fractionating intralysosomal soluble proteins by velocity sedimentation on sucrose gradients or gel permeation chromatography we identified a thyroid arylsulfatase A holoenzyme which corresponds to a 120,000 Mr species. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analyses of the gradient or column fractions showed that the 120-kDa protein peak with arylsulfatase A activity essentially contained the 58- and 54-kDa polypeptides in equivalent amounts. In conclusion, arylsulfatase A, a heterodimer of 120 kDa composed of two nonidentical subunits, is the major protein component of thyroid lysosomes. The superabundance of this protein in purified thyroid lysosomes is related to the very high specific activity of the enzyme in the thyroid as compared to other tissues.     

A specific ultrastructural stain for arylsulfatase A activity in human cultured fibroblasts

A staining reaction was developed to specifically detect arylsulfatase A activity in the presence of arylsulfatases B and C. Nitrocatechol, generated by all arylsulfatases from the substrate p-nitrocatechol sulfate, can be coupled to produce Hatchett 's brown which reacts with 3,3'-diaminobenzidine to yield an osmiophilic polymer visible under the electron microscope. The reaction was made specific for arylsulfatase A by inhibiting arylsulfatase C activity with low pH and arylsulfatase B activity with pyrophosphate. The specificity was confirmed both by electrophoretic analysis and by patient fibroblasts deficient only in arylsulfatase A activity. Under optimal conditions for preserving structural integrity and enzyme activity, enzyme reaction deposits were found mainly around vesicles. Some of these vesicles were large and heterogeneous (48-330 nm in diameter), distributed randomly within the cytoplasm, but most of the positive-reacting vesicles were uniform in size (86 +/- 18 nm in diameter) and distributed in a peripheral zone about 0.1-0.5 micron wide. These periplasmic vesicles might be partly fused with each other or with the plasma membrane. In conclusion, a specific stain for arylsulfatase A activity suitable for light and electron microscopy and the optimal conditions for structural and enzymatic preservations were developed. Although this enzyme has been considered to be lysosomal in origin, most of the activity was detected in periplasmic vesicles near the cell surface.     

Synthesis and processing of arylsulfatase A in human skin fibroblasts

Biosynthesis of arylsulfatase A in normal and mutant human fibroblasts was studied by growing cells in the presence of L-[4,5-3H] leucine or [2-3H] mannose, isolation of labelled arylsulfatase A by immune precipitation and visualization of electrophoretically separated polypeptide by fluorography. Arylsulfatase A was synthesized as a precursor with a mean apparent molecular mass of 62 kDa. Intracellularly the precursor was converted into a 60.5 kDa polypeptide within a chase period of 1 to 7 days. The 60.5 kDa product in polyacrylamide corresponded to one of two polypeptides present in arylsulfatase A isolated from human placenta. In fibroblasts from a patient with metachromatic leukodystrophy no immune precipitable polypeptides of arylsulfatase A were detected. In normal fibroblasts less than 10% of the precursor of arylsulfatase A was secreted into the medium, whereas in mucolipidosis II fibroblasts and in control fibroblasts grown in the presence of NH4Cl up to 90% of the precursor of arylsulfatase A, appeared in the medium and remained there without change in the apparent molecular mass for at least 7 days. Arylsulfatase A polypeptides appear to contain two carbohydrate side chains. In about 90% of the polypeptides both side chains are cleaved by endo-beta-N-acetylglucosaminidase H, whereas in the remaining chains one of the two oligosaccharides is not cleaved.     

Differentiation between arylsulfatase A deficiency and pseudo-deficiency

Metachromatic leukodystrophy (MLD)--lysosomal storage disease caused arylsulfatase A (ARSA) deficiency. Biochemical diagnostic of MLD is complicated by arylsulfatase A pseudodeficiency. There is possibility of mistake in MLD diagnoses in case of pseudodeficiency ARSA and non-MLD neurological disease combination. We suggest the new modification of arylsulfatase A activity detection method which allows to identify the arylsulfatase A pseudodeficiency without molecular genetic methods.     

Phosphorylation and sulfation of arylsulfatase A accompanies biosynthesis of the enzyme in normal and carcinoma cell lines

Arylsulfatase A (arylsulfate sulfohydrolase, EC 3.1.6.1), a mammalian lysosomal enzyme, is initially synthesized as a 69, 67 and 64 kDa precursor polypeptide in a prostate carcinoma cell line PC-3SF12, in HeLa cells and in a normal human embryonic lung cell line WI-38, respectively. These precursor polypeptides are secreted into the medium or processed to mature enzymes of apparent molecular mass 66, 64 or 62 kDa in PC-3SF12, HeLa or WI-38 cells, respectively. The precursor and mature polypeptides in WI-38 cells are phosphorylated, and the phosphate is lost upon treatment with endo-beta-hexosaminidase H. Arylsulfatase A is also shown to be sulfated in WI-38 cells. The presence of castanospermine, an inhibitor of sulfation of the second N-acetylglucosamine residue of the chitobiose core, does not reduce the extent of sulfation of arylsulfatase A, suggesting that either terminal sugars or the protein is sulfated. Sulfation may have a protective function similar to that of terminal sialic acid residues in glycoproteins. Although the subcellular location of arylsulfatase A is identical in PC-3SF12 and in WI-38 cells, pulse-chase experiments indicate that arylsulfatase A protein has a slower turnover in the prostate carcinoma cell line than it does in the normal human lung cell line. The differences in the apparent molecular weights of arylsulfatase A in the normal and carcinoma cell lines are shown to be due to variations in the carbohydrate content of the enzyme. The apparent molecular mass of the polypeptide chain obtained after endo-beta-hexosaminidase H treatment is 59 kDa, a value which is identical for all three cell lines studied here. These results suggest the possibility of an enhanced activity of terminal glucosyltransferase enzymes in carcinoma cell lines and in tumor tissues. Arylsulfatase A may be a useful marker for studying transformation-related processes in human cell lines.     

Deficient glycosylation of arylsulfatase A in pseudo arylsulfatase-A deficiency

Summary Deficient arylsulfatase-A activity is diagnostic of a neurodegenerative human lysosomal storage disease, metachromatic leukodystrophy. Paradoxically, similar enzyme deficiency also occurs in normal individuals, who are known as being pseudo arylsulfatase-A deficient. We showed previously that this phenotype is associated with a structural gene mutation that produces an exceptionally labile enzyme. We now report on the nature and consequence of this mutation. When the mutant arylsulfatase-A is deglycosylated by endoglycosidase H, only one smaller molecular species was generated, instead of the two from the normal enzyme. This is consistent with the loss of one of the two N-linked oligosaccharide side chains known to be present on the wild-type enzyme. Quantitative analysis of mannose and leucine incorporation showed that the mutant enzyme incorporated two- to tenfold less mannose than the normal enzyme on a molar basis. This deficient glycosylation was specific to arylsulfatase-A. Another lysosomal enzyme not affected in this mutation, beta-hexosaminidase, was glycosylated normally in the mutant cells. The remaining single oligosaccharide side chain released from the mutant arylsulfatase-A by pronase digestion was normally processed to complex and high-mannose forms. However, the high-mannose side chains contained 30% fewer phosphorylated residues than those of the normal enzyme. Nevertheless, this reduced level of phosphorylation did not prevent targeting of the mutant enzyme to the lysosomes, a process normally mediated through phosphorylated mannose residues. In conclusion, pseudo arylsulfatase-A deficiency is a unique human mutation associated with reduced glycosylation and phosphorylation of a lysosomal enzyme with the loss of one of the two carbohydrate side chains. The mutation results in greatly reduced enzyme stability, thus indicating a role for oligosaccharides in maintaining enzyme stability within the degradative environment of the lysosomes. However, the residual catalytic activity or subcellular targeting of the mutant enzyme was not affected. These properties probably account for the benign clinical presentation of pseudo arylsulfatase-A deficiency.Abbreviations PD Pseudo arylsulfatase-A Deficiency - ARA Arylsulfatase-A     

Cloning and expression of human arylsulfatase A

A full length cDNA for human arylsulfatase A was cloned and sequenced. The predicted amino acid sequence comprises 507 residues. A putative signal peptide of 18 residues is followed by the NH2-terminal sequence of placental arylsulfatase A. One of the arylsulfatase A peptides ends 3 residues ahead of the predicted COOH terminus. This indicates that proteolytic processing of arylsulfatase A is confined to the cleavage of the signal peptide. The predicted sequence contains three potential N-glycosylation sites, two of which are likely to be utilized. The sequence shows no homology to any of the known sequences of lysosomal enzymes but a 35% identity to human steroid sulfatase. Transfection of monkey and baby hamster kidney cells resulted in an up to 200-fold increase of the arylsulfatase A activity. The arylsulfatase A was located in lysosome-like structures and transported to dense lysosomes in a mannose 6-phosphate receptor-dependent manner. The arylsulfatase A cDNA hybridizes to 2.0- and 3.9-kilobase species in RNA from human fibroblasts and human liver. RNA species of similar size were detected in metachromatic leukodystrophy fibroblasts of two patients, in which synthesis of arylsulfatase A polypeptides was either detectable or absent.     

Mucopolysaccharidosis VI (Maroteaux-Lamy syndrome). An intermediate clinical phenotype caused by substitution of valine for glycine at position 137 of arylsulfatase B.

The Maroteaux-Lamy syndrome (mucopolysaccharidosis type VI) is a lysosomal storage disease with autosomal recessive inheritance caused by deficiency of the enzyme arylsulfatase B. Severe, intermediate, and mild forms of the disease have been described. The molecular correlate of the clinical heterogeneity is not known at present. To identify the molecular defect in a patient with the intermediate form of the disease, arylsulfatase B mRNA from his fibroblasts was reverse-transcribed, amplified by the polymerase chain reaction, and subcloned. Three point mutations were detected by DNA sequence analysis, two of which, a silent A to G transition at nucleotide 1191 and a G to A transition at nucleotide 1126 resulting in a methionine for valine 376 substitution, were polymorphisms. A G to T transversion at nucleotide 410 causing a valine for glycine 137 substitution (G137V) was identified as the mutation underlying the Maroteaux-Lamy phenotype of the patient, who was homozygous for the allele. The kinetic parameters of the mutant arylsulfatase B enzyme toward a radiolabeled trisaccharide substrate were normal excluding an alteration of the active site. The G137V mutation did not affect the synthesis but severely reduced the stability of the arylsulfatase B precursor. While the wild type precursor is converted by limited proteolysis in late endosomes or lysosomes to a mature form, the majority of the mutant precursor was degraded presumably in a compartment proximal to the trans Golgi network and only a small amount escaped to the lysosomes accounting for the low residual enzyme activity in fibroblasts of a patient with the juvenile form of the disease.     

Isolation and comparison of arylsulfatase A from rat liver and Morris hepatoma 7777

Rat liver and Morris hepatoma 7777 arylsulfatase A were isolated from the soluble lysosomal extract by a procedure involving blue-Sepharose affinity chromatography, DEAE-cellulose chromatography, hydrophobic chromatography on phenyl-Sepharose and preparative polyacrylamide gel electrophoresis. The preparation obtained by this method was apparently homogenous in disc electrophoresis and in immunoelectrophoresis. The comparative studies revealed that the properties of arylsulfatase A from rat liver and Morris hepatoma 7777 are very similar, considering molecular weight of the native monomer and its subunits, the ability to form tetramers, isoelectric point, Michaelis constant and the anomalous kinetics of the reaction. The twofold elevation of arylsulfatase B activity found in Morris hepatoma 7777 suggests that the enzyme may have certain functions in tumor growth.     

Synthesis of pyrene derivatives of cerebroside sulfate and their use for determining arylsulfatase A activity

Two fluorescent derivatives of cerebroside sulfate ('sulfatide') have been synthesized and used as substrates for determining arylsulfatase A activity. These were 12-(1-pyrene)dodecanoyl cerebroside sulfate (P12-sulfatide) and 12(1-pyrenesulfonylamido)dodecanoyl cerebroside sulfate (PSA12-sulfatide). When incubated at pH 5.0 in the presence of 5 mM MnCl2 and 5.5 mM of taurodeoxycholate, either substrate was hydrolyzed by arylsulfatase A of human leukocytes. The rate of hydrolysis was proportional to the incubation time and concentration of enzyme; Michaelis-Menten type kinetics were observed with increasing concentrations of substrate. For determining the rate of hydrolysis, each of the two products (i.e., P12- and PSA12-cerebrosides) were separated from the bulk of respective unreacted sulfatide on small columns of DEAE-Sephadex A-25 and their fluorescence intensities read at 343-378 and 350-380 nm for the excitation and emission wavelengths for P12- and PSA12-cerebrosides, respectively. When extracts of skin fibroblasts derived from normal individuals and patients with Maroteaux-Lamy (lacking arylsulfatase B) or metachromatic leukodystrophy (lacking arylsulfatase A) were used as source of enzyme, P12-sulfatide was hydrolyzed by the former two but not by the latter cell extract. Several derivatives of cerebroside sulfate were also synthesized and found to inhibit the hydrolysis of pyrenesulfatide by leukocyte arylsulfatase A. The results demonstrate that these two pyrene containing sulfatides can be effectively used as specific substrates for the determination of arylsulfatase A activity in extract of cells and most probably also of tissues.