An assay for iduronate sulfatase (Hunter corrective factor)

Functional assessment of the genetic findings indicating mucopolysaccharidosis type II in the prenatal setting

Mucopolysaccharidosis type II (MPS II) is a multi-systemic disorder arising due to pathogenic variants in the gene located on chromosome Xq28 encoding the lysosomal enzyme, iduronate 2-sulfatase (IDS). The broad clinical heterogeneity of MPS II can be partly ascribed to the high level of molecular diversity in the gene locus with the majority of variants localised within one family. Here, we describe a case of fetal hepatomegaly that was causatively investigated for 151 genes associated with fetal hydrops and lysosomal diseases. Sequence analysis identified a novel hemizygous variant, pAsp532Gly, in exon 9 of the IDS gene. Determination of IDS activity in cultured amniotic fluid cells returned 8% of normal activity and analysis of a second sulfatase was normal, the latter virtually excluding multiple sulfatase deficiency. Together, these data supported a diagnosis of MPS II in the fetus. Additional measurement of a signature disaccharide in the amniotic fluid was normal, conflicting with enzymology indications. The baby was unremarkable at birth and 3 years later shows no clinical suspicion of MPS II, normal urinary disaccharide concentrations, and reduced IDS activity in leukocytes. His 5-year-old brother was subsequently shown to carry the same pAsp532Gly variant, with normal urinary disaccharide concentrations, reduced leukocyte IDS activity and normal phenotype. This case highlights the importance of thorough biochemical investigations, clinical and family correlation in determining the significance of genetic variants in IDS.

Research and Application of Chondroitin Sulfate/Dermatan Sulfate-Degrading Enzymes

Chondroitin sulfate (CS) and dermatan sulfate (DS) are widely distributed on the cell surface and in the extracellular matrix in the form of proteoglycan, where they participate in various biological processes. The diverse functions of CS/DS can be mainly attributed to their high structural variability. However, their structural complexity creates a big challenge for structural and functional studies of CS/DS. CS/DS-degrading enzymes with different specific activities are irreplaceable tools that could be used to solve this problem. Depending on the site of action, CS/DS-degrading enzymes can be classified as glycosidic bond-cleaving enzymes and sulfatases from animals and microorganisms. As discussed in this review, a few of the identified enzymes, particularly those from bacteria, have wildly applied to the basic studies and applications of CS/DS, such as disaccharide composition analysis, the preparation of bioactive oligosaccharides, oligosaccharide sequencing, and potential medical application, but these do not fulfill all of the needs in terms of the structural complexity of CS/DS.

Mucopolysaccharidosis type II (Hunter syndrome): Clinical and biochemical aspects of the disease and approaches to its diagnosis and treatment

Mucopolysaccharidosis type II (MPS II, Hunter syndrome) is a rare X-linked lysosomal storage disease caused by mutations of the gene encoding the lysosomal enzyme iduronate-2-sulfatase (IDS), the role of which is to hydrolytically remove O-linked sulfates from the two glycosaminoglycans (GAGs) heparan sulfate (HS) and dermatan sulfate (DS). HS and DS are linear, heterogeneous polysaccharides composed of repeating disaccharide subunits of l-iduronic acid (IdoA) or d-glucuronic acid, (1→4)-linked to d-glucosamine (for HS), or (1→3)-linked to 2-acetamido-2-deoxy-d-galactose (N-acetyl-d-galactosamine) (for DS). In healthy cells, IDS cleaves the sulfo group found at the C-2 position of terminal non-reducing end IdoA residues in HS and DS. The loss of IDS enzyme activity leads to progressive lysosomal storage of HS and DS in tissues and organs such as the brain, liver, spleen, heart, bone, joints and airways. Consequently, this leads to the phenotypic features characteristic of the disease. This review provides an overview of the disease profile and clinical manifestation, with a particular focus on the biochemical basis of the disease and chemical approaches to the development of new diagnostics, as well as discussing current treatment options and emerging new therapies.

Mutation analysis in 57 unrelated patients with MPS II (Hunter's disease)

Genomic DNA from 57 unrelated MPS II (Hunter's disease) patients was analysed for mutations of the iduronate sulphatase (IDS) gene. The aim of the study was threefold: to identify the primary genetic lesion in patients, to investigate the correlation between genotype and phenotype, and most importantly, to provide reliable carrier testing for female members once the family mutation was identified. In 42 patients, point mutations were identified involving single base substitutions, deletions, or insertions. These included four new nonsense mutations (R8X, C84X, E245X, Y466X), six new missense mutations (D45N, N115Y, P228L, P266R, E434K, I485K, W502C), three new insertions (c70C71ins, c652C654ins, c709G710ins), six new deletions (c500delC, c705delC, c1023delA, c1049delA, c1141delC, c1576delG), and five new mutations involving splice sites (IVS1-2 a-->g, IVS2-10 t-->g, IVS5 + 2 t-->g L236L, IVS7 + 2 t-->c). One patient had a new seven base deletion in exon 9 (c1482-1488del). Four patients were shown to have complete deletions of the IDS gene and two deletions involved one or more exons. Previously described mutations present in these patients were Q80X, P86L, R172X, G374G, S333L, R443X, and R468Q. In eight patients, no mutation was detected throughout the entire coding region. Most mutations that result in MPS II appear to be unique. Absence of the probands' mutations in eight of nine maternal grandmothers suggests many mutations have arisen recently. Prediction of the clinical phenotype from the identified genotype was difficult in some families, and further studies using reverse transcription polymerase chain reaction are needed to confirm the predicted effects on the IDS mRNA suggested by genomic analysis.

The clinical phenotype of two patients with a complete deletion of the iduronate-2-sulphatase gene (mucopolysaccharidosis II--Hunter syndrome)

Two patients with a complete deletion of the iduronate-2-sulphatase (IDS) gene are described. In both patients, the resulting phenotype was that of very severe Hunter syndrome (mucopolysaccharidosis II). In addition, both had features not commonly seen in this disorder, e.g. early onset of seizures in one patient and ptosis in the other. It is speculated that loss of adjacent loci may contribute to the unusual findings and that the severe features present in both patients may represent contiguous gene syndromes. Further analysis of IDS cDNA from other patients with Hunter's syndrome may eventually enable phenotype to be predicted more accurately.

Human liver glucuronate 2-sulphatase. Purification, characterization and catalytic properties

Human glucuronate 2-sulphatase (GAS), which is involved in the degradation of the glycosaminoglycans heparan sulphate and chondroitin 6-sulphate, was purified almost 2,000,000-fold to homogeneity in 8% yield from liver with a four-step six-column procedure, which consists of a concanavalin A-Sepharose/Blue A-agarose coupled step, a DEAE-Sephacel/octyl-Sepharose coupled step, CM-Sepharose chromatography and gel-permeation chromatography. Although more than 90% of GAS activity had a pI of greater than 7.5, other forms with pI values of 5.8, 5.3, 4.7 and less than 4.0 were also present. The pI greater than 7.5 form of GAS had a native molecular mass of 63 kDa. SDS/polyacrylamide-gel-electrophoretic analysis resulted in two polypeptide subunits of molecular mass 47 and 19.5 kDa. GAS was active towards disaccharide substrates derived from heparin [O-(beta-glucuronic acid 2-sulphate)-(1----4)-O-(2,5)-anhydro[1-3H]mannitol 6-sulphate (GSMS)] and chondroitin 6-sulphate [O-(beta-glucuronic acid 2-sulphate-(1----3)-O-(2,5)-anhydro[1-3H]talitol 6-sulphate (GSTS)]. GAS activity towards GSMS and GSTS was at pH optima of 3.2 and 3.0 respectively with apparent Km values of 0.3 and 0.6 microM respectively and corresponding Vmax values of 12.8 and 13.7 mumol/min per mg of protein respectively. Sulphate and phosphate ions are potent inhibitors of enzyme activity. Cu2+ ions stimulated, whereas EDTA inhibited enzyme activity. It was concluded that GAS is required together with a series of other exoenzyme activities in the lysosomal degradation of glycosaminoglycans containing glucuronic acid 2-sulphate residues.

Normal excretion of urinary acid mucopolysaccharides in a boy with iduronate sulphatase deficiency, Hunter phenotype and alpha 1-antitrypsin deficiency

The chance coincidence of an X-linked disorder with an autosomal recessive disorder in one child is described. The child had the clinical phenotype of a mucopolysaccharidosis and the activity of iduronate sulphatase was almost absent. Furthermore, fibroblasts from a typical Hunter patient were unable to correct the patient's fibroblasts. However, three 24 h urine samples collected at 18-36 months of age showed a nearly normal excretion of acid mucopolysaccharides. The boy died in liver coma at 3 years of age. Autopsy showed cirrhosis of the liver and changes in liver tissue consistent with alpha 1-antitrypsin deficiency.

Full expression of Hunter's disease in a female with an X-chromosome deletion leading to non-random inactivation

A 2.5-year-old girl who presented with abdominal distension, hepatomegaly, coarse facies, hirsutism and contraction deformities was investigated for mucopolysaccharidoses. Urinary excretion showed increased total glycosaminoglycans (105 mg/mmol creatinine; normal for age 9-20 mg/mmol) with marked increases of dermatan and heparan sulphates. A number of lysosomal enzyme activities were measured on leucocytes, serum and cultured fibroblasts. Normal or high activities were found for alpha-iduronidase, N-acetylgalactosamine-6-sulphatase, beta-galactosidase, arylsulphatase B and beta-glucuronidase. However a marked deficiency of iduronate sulphate sulphatase activity was observed, consistent with a diagnosis of Hunter's disease. Activities were reduced to less than 2% of mean control values in the patient's leucocytes, serum and cultured fibroblasts. Normal activities were measured in samples from the father and younger sister but a partial deficiency (43% of control serum) was found in the mother. Chromosome studies on the patient revealed a partial deletion of the long arm of one X-chromosome, most probably of band Xq25, which was not inherited from either parent. Studies using BrdU indicated that the deleted X chromosome was consistently late replicating, and as a result the Hunter gene was fully expressed on the other X chromosome.

Heparin trisaccharides with nonreducing 2-amino-2-deoxy-alpha-D-glucopyranosyl end-groups suitable as substrates for catabolic enzymes

Heparin trisaccharides having the sequence O-(2-amino-2-deoxy-alpha-D-glucopyranosyl)-(1----4)-O-alpha-L- idopyranosyluronic acid-(1----4)-2,5-anhydro-D-[1-3H]mannitol have been prepared, as substrate models for studying sulfatases of heparan sulfate catabolism, by alpha-L-iduronidase cleavage of previously reported heparin tetrasaccharides, with additional chemical and enzymic modification as required. Three series are described, including isomeric sulfate esters of that trisaccharide with no N-substituent, with N-acetyl substitution, and with N-sulfate substitution. New features of the substrate specificity of the hydrolases used, including iduronate sulfatase, alpha-L-iduronidase, glucosamine 6-sulfate sulfatase, and heparin sulfamidase, were observed, and simple procedures for partial purification of these hydrolases are reported. The structures assigned to the trisaccharides are supported by the mode of preparation, reactions, regularities in electrophoretic behavior, and identities of the products of deamination.

Sequence variation in heparin octasaccharides with high affinity for antithrombin III

We have isolated from nitrous acid cleavage products of heparin two major octasaccharide fragments which bind with high affinity to human antithrombin. Octasaccharide S, with the predominant structure iduronic acid----N-acetylglucosamine 6-O-sulfate----glucuronic acid-----N-sulfated glucosamine 3,6-di-O-sulfate----iduronic acid 2-O-sulfate----N-sulfated glucosamine 6-O-sulfate----iduronic acid 2-O-sulfate----anhydromannitol 6-O-sulfate, is sensitive to cleavage by Flavobacterium heparinase as well as platelet heparitinase and binds to antithrombin with a dissociation constant of (5-15) X 10(-8) M. Octasaccharide R, with the predominant structure iduronic acid 2-O-sulfate----N-sulfated glucosamine 6-O-sulfate----iduronic acid----N-acetylglucosamine 6-O-sulfate----glucuronic acid----N-sulfated glucosamine 3,6-di-O-sulfate----iduronic acid 2-O-sulfate----anhydromannitol 6-O-sulfate, is resistant to degradation by both enzymes and binds antithrombin with a dissociation constant of (4-18) X 10(-7) M. The occurrence of a 15-17% replacement of N-sulfated glucosamine 3,6-di-O-sulfate with N-sulfated glucosamine 3-O-sulfate and a 10-12% replacement of iduronic acid with glucuronic acid in both octasaccharides indicates that these substitutions have little or no effect on the binding of the oligosaccharides to the protease inhibitor. When bound to antithrombin, both octasaccharides produce a 40% enhancement in the intrinsic fluorescence of the protease inhibitor and a rate of human factor Xa inhibition of 5 X 10(5) M-1 s-1 as monitored by stopped-flow fluorometry. This suggests that the conformation of antithrombin in the region of the factor Xa binding site is similar when the protease inhibitor is complexed with either octasaccharide.

Structural studies on heparin. Tetrasaccharides obtained by heparinase degradation

Three tetrasaccharides representing major structural sequences of heparin were isolated in good yield and characterized after degradation of heparin by purified flavobacterial heparinase. N-Desulfation was necessary to achieve good separation of these closely related compounds from each other. One of the tetrasaccharides was shown to be derived from the fully sulfated repeating segments; to contain L-iduronic acid and six sulfate groups, and have the structure delta 4,5- HexpA -(2-SO4)-(1----4)-alpha-D- GlcpN -(N-SO4)-(6-SO4)-(1- ---4)-alpha -L- IdopA -(2-SO4)-(1----4)-D- GlcN -(N-SO4)-(6-SO4). The second contained a D-glucuronic acid unit that was nonsulfated instead of the L-iduronic acid, and the third, obtained in a fairly low yield, contained five sulfate groups, three of which being located on the disaccharide at the nonreducing end, and having the structure delta 4,5- HexpA -(2-SO4)-(1----4)-alpha-D- GlcpN -(N-SO4)-(6-SO4)-(1- ---4)-alpha -L- IdopA -(2-SO4)-(1----4)-D- GlcN -(N-SO4). All tetrasaccharides had a sulfated, unsaturated uronic acid unit at the nonreducing end, confirming that the heparinase requires sulfated L-iduronic acid units for activity.

Selective depolymerisation of dermatan sulfate: production of radiolabelled substrates for alpha-L-iduronidase, sulfoiduronate sulfatase, and beta-D-glucuronidase

Radiolabelled disaccharide substrates for alpha-L-iduronidase, beta-D-glucuronidase, and sulfoiduronate sulfatase have been prepared from dermatan sulfate by application in sequence of N-deacetylation, deaminative cleavage, and reduction with NaBT4. The yield of disaccharides was approximately 87% of the total oligosaccharide fraction. Five disaccharides were isolated and tentatively identified. The major disaccharide, O-(alpha-L-idopyranosyluronic acid)-(1 leads to 3)-2,5-anhydro-D-[1-3H]talitol 4-sulfate (IdoA-anT4S), represented approximately 75% of the total disaccharide fraction. The other disaccharides were O-(alpha-L-idopyranosyluronic acid 2-sulfate)-(1 leads to 3)-2,5-anhydro-D-[1-3H]talitol 4-sulfate (IdoA2S-anT4S), O-(beta-D-glucopyranosyluronic acid)-(1 leads to 3)-2,5-anhydro-D-[1-3H]talitol 4-sulfate (GlcA-anT4S), O-(beta-D-glucopyranosyluronic acid)-(1 leads to 3)-2,5-anhydro-D-[1-3H]talitol 6-sulfate (GlcA-anT6S), and O-(alpha-L-idopyranosyluronic acid)-(1 leads to 3)-2,5-anhydro-D-[1-3H]talitol (IdoA-anT), which represented approximately 4.5, 11.2, 1.0, and 1.8%, respectively, of the total disaccharide fraction. When incubated with cultured skin-fibroblasts from normal controls, IdoA-anT4S was shown to be a sensitive substrate for alpha-L-iduronidase to produce 2,5-anhydro-D-talitol 4-sulfate (anT4S). Activity toward IdoA-anT4S was not observed with fibroblast homogenates from alpha-L-iduronidase-deficient patients (Mucopolysaccharidosis Type I). Similarly, normal-fibroblast homogenates degraded GlcA-anT6S to anT6S, and GlcA-anT4S to anT4S, at a rate 6 to 8 times greater than found for fibroblasts from beta-D-glucuronidase-deficient patients (Mucopolysaccharidosis Type VII). IdoA-anT4S was hydrolysed by alpha-L-iduronidase at a rate 365 times greater than that for IdoA-anT. Sulfation of the anhydro-D-[1-3H]talitol residues is an important structural determinant in the mechanism of action of alpha-L-iduronidase on disaccharide substrates. IdoA2S-anT4S was degraded to IdoA-anT4S and then to anT4S by normal-fibroblast homogenates, whereas fibroblasts from alpha-L-iduronidase-deficient and sulfoiduronate sulfatase-deficient (Mucopolysaccharidosis Type II) patients produced considerably decreased levels of anT4s and IdoA-anT4S (and anT4S), respectively.

Activities of sulfatases for the degradation of acidic glycosaminoglycans in cultured skin fibroblasts from two siblings with multiple sulfatase deficiency

Cultured skin fibroblasts from two siblings with multiple sulfatase deficiency (MSD) were assayed for the activities of sulfatases known to degrade acidic glycosaminoglycans (AGAG). There were iduronate sulfatase, arylsulfatase B, heparan sulfate (HS) sulfatase, N-acetylgalactosamine-6-sulfate sulfatase, HS-derived N-acetylglucosamine-6-sulfate sulfatase, and two keratan sulfate (KS)-derived N-acetylglucosamine-6-sulfate sulfatases. The activities of sulfatases required for the degradation of HS were reduced to a greater extent than those for the degradation of dermatan sulfate (DS), and those of sulfatases associated with basic defect of Morquio disease type A were moderately decreased or normal. On the other hand, urinary excretion of AGAG in both patients was increased about 10-fold compared to controls, and especially, the excretion of HS and DS was increased about 150-fold and 50-fold, respectively. Keratan sulfate was not detected. The results suggest that in patients with MSD the degradation of HS might be affected to a greater extent than that of DS.

The iduronate sulphatase activities of cells and tissue fluids from patients with Hunter syndrome and normal controls

The substrate O-(alpha-L-idopyranosyluronic acid-2-sulphate)-(1 leads to 4)-2,5-anhydro-D-(3H-1) mannitol-6-sulphate was used at a final concentration of 50 mmol/l to measure the alpha-L-idurono-2-sulphate sulphatase activities of cell extracts, serum and amniotic fluid. Activities were measured after dialysis against water, to avoid the inhibitory effect of sodium chloride and the reaction products separated by ion-exchange chromatography on ECTEOLA cellulose. The enzyme present in normal serum had an apparent Km of 0.12 mmol/l. The mean activities of normal serum, fibroblasts and leukocytes were 0.61, 16.63 and 18.75 nmol/mg protein per hour respectively, while corresponding 'Hunter' tissues contained between 1% and 3% of normal activity. Cultured normal amniotic cells had a mean activity of 8.46 nmol/mg protein per hour, while those cultured from 'Hunter' patients contained about 6% of normal activity. Hunter disease can thus be readily diagnosed in a wide variety of tissues. Samples from three obligate heterozygotes were found to have iduronate sulphatase activities amounting to 41%, 57% and 63% of normal values.

The mucopolysaccharidoses: a synergism between clinical and basic investigation

The mucopolysaccharidoses are a family of genetic diseases involving faulty degradation of one or more type of mucopolysaccharide or glycosaminoglycan. These conditions are characterized by skeletal, connective tissue, and intellectual manifestations. Biochemical investigations over the past 10-20 yr have enhanced our understanding of the clinical conditions and advanced our knowledge of catabolic pathways for complex biological structures. Identification of stored and excreted materials as partially degraded glycosaminoglycans allowed classification of these conditions on clinical and chemical criteria. The development of a cell culture model for studying the mucopolysaccharidoses lead to the identification of a variety of lysosomal sulfatases and glycosidases as deficient enzymes. This stimulated the identification of several new conditions. Knowledge of primary biochemical defects improved genetic services by providing accurate diagnosis, facilitating carrier identification and improving prenatal diagnosis. Glycosaminoglycan excretion patterns associated with individual enzyme defects suggested sequential degradative pathways for GAGs and related macromolecules. Attempts at enzyme replacement revealed a complex system of recognition markers and membrane receptors for the uptake of extracellular proteins. Multiple enzyme deficiencies are providing information on lysosomal enzyme synthesis and processing. The mucopolysaccharide storage diseases offer an excellent example of a productive synergism between basic biology and clinical medicine.

Properties of sulfatases in cultured skin fibroblasts of multiple sulfatase deficient patients

Various sulfatase activities were assayed in cultured skin fibroblasts from patients with multiple sulfatase deficiency (MSD). MSD cell lines displayed deficiencies of arylsulfatase A and iduronate sulfatase, but activities of arylsulfatase B, N-acetylgalactosamine 6-sulfate sulfatase and N-acetylglucosamine 6-sulfate sulfatase were within normal ranges, but not consistently. Arylsulfatase A, minor anionic arylsulfatase and N-acetylgalactosamine 6-sulfate sulfatase in MSD cell lines had similar Km, pH optima, inhibitory or activator sensitivity to that of normal skin fibroblasts. Arylsulfatase B in MSD cell lines also had properties similar to that of normal skin fibroblasts, except an abnormal heat stability. From our results, we conclude that properties of arylsulfatase A, minor anionic arylsulfatase and N-acetylgalactosamine 6-sulfate sulfatase in MSD fibroblasts were intact. On the other hand, arylsulfatase B in MSD might be a functionally abnormal enzyme.

Selective depolymerisation of heparin to produce radio-labelled substrates for sulfamidase, 2-acetamido-2-deoxy-alpha-D-glucosidase, acetyl-CoA:2-amino-2-deoxy-alpha-D-glucoside N-acetyltransferase, and 2-acetamido-2-deoxy-D-glucose 6-sulfate sulfatase

Heparin was carboxyl-reduced with NaBT4, and degraded under conditions of acid hydrolysis that selectively cleaved the 2-0-sulfo-L-idopyranosidic linkages. The resulting, radiolabelled-disaccharides and -tetrasaccharides were isolated by gel chromatography, and then fractionated by ion-exchange chromatography, paper chromatography, and paper electrophoresis. Of the nine disaccharides isolated and identified, eight were probably derived from the major repeating-disaccharide unit in heparin (2-deoxy-2-sulfoamino-D-glucosyl 6-sulfate leads to L-idosyluronic acid 2-sulfate). Sodium borotritide reduction and/or HNO2 deamination of these eight disaccharide fractions indicated four to contain L-idopyranose residues and the other four to contain 1,6-anhydro-L-idopyranose residues as terminal units. The latter, terminal unit probably represents a minor component formed during the acid hydrolysis. On the basis of N-acetylation, N-sulfation, and HNO2-deamination studies, and the known positions and configurations of the glycosidic and sulfate linkages in heparin, four disaccharides were identified as 0-(2-amino-2-deoxy-alpha-D-glucopyranosyl)-(1 leads to 4)-L-[6-3H]idopyranose, 0-(2-amino-2-deoxy-alpha-D-glycopyranosyl)-(1 leads to 4)-L-[6-3H]idopyranose 2-sulfate, and 0-(2-amino-2-deoxy-alpha-D-glucopyranosyl 6-sulfate]-(1 leads to 4)-L-[6-3H]idopyranose 2-sulfate. A similar set of four disaccharides contained 1,6-anhydro-L-[6-3H]idopyranose residues in place of the L-[6-3H]idopyranose residues. The other disaccharide was tentatively identified as 0-(2-acetamido-2-deoxy-alpha-D-glucopyranosyl)-(1 leads to 4)-L-[6-3H]idopyranose, the isolation of which suggests the presence of an IdA(OSO-3)-GlcNAc-IdA(OSO-3) sequence in the heparin preparation, which accounts for at least 1% of its total sequence. The tetrasaccharides were fractionated, on the basis of their sulfate content, into at least five species by ion-exchange chromatography or by paper electrophoresis. These were fractionated further into species with and without carboxyl groups, and with L-idopyranose or 1,6-anhydro-L-idopyranose residues as terminal units. Tentative structures for some of these tetrasaccharides are proposed. Disaccharide and tetrasaccharide species were evaluated before and after N-acetylation or N-sulfation, as substrates for sulfamidase, acetyl-CoA: 2-amino-2-deoxy-alpha-D-glucoside N-acetyl-transferase, 2-acetamido-2-deoxy-alpha-D-glucosidase, or 2-acetamido-2-deoxy-D-glucose 6-sulfate sulfatase in human-skin fibroblasts.

An improved assay for iduronate 2-sulphate sulphatase in serum and its use in the detection of carriers of the Hunter syndrome

A more sensitive assay procedure has been developed for the enzyme iduronate 2-sulphate sulphatase which is deficient in the Hunter syndrome. The substrate is the same as previously described by Lim et al. [1], O-(alpha-L-idopyranosyluronic acid 2-sulphate)-(1leads to 4)-2,5 anhydro-D-[3H-1]mannitol 6-sulphate, but, after incubation, it is separated from the product by ion-exchange chromatography on a micro-column of Dowex 1 x 2 (Cl-1) instead of high voltage electrophoresis or ECTEOLA cellulose chromatography. Since the blank correction is then much smaller, a shorter incubation time can be used and conversion of the substrate reduced from approximately 50% down to levels where complications resulting from substrate depletion and product inhibition are minimal. Using whole serum the apparent Km for the substrate is 0.2 mmol/l. With an incubation time of 20 min, sera from heterozygotes exhibited approximately 35% of the normal levels of iduronate 2-sulphate sulphatase (0.11-0.61, mean 0.34 nmol.h-1.mg-1 protein for carriers; 0.24-2.35, mean 0.94 nmol.h-1.mg-1 protein for 37 normal females). Serum analyses can thus be used to supplement those on hair roots in the detection of carriers of the Hunter syndrome.

Lumbar kyphosis in Hunter's disease (MPS ii)

Although radiological involvement of the lower dorsal and upper lumbar vertebrae is common in the severe form of Hunter's disease (MPS II), there are reports in the literature that clinical kyphosis does not occur. We report a boy with marked clinical kyphosis in whom the diagnosis of MPS II was proved by demonstrating a severe deficiency of serum and leucocyte iduronate-sulphate sulphatase and an accelerated incorporation of radiosulphate into his cultured fibroblast glycosaminoglycans, which could not be corrected by the product of other typed reference MPS II cells. The existence of several other genetic diseases, sometimes complicated by kyphosis, was excluded by assay of fibroblast lysosomal enzymes.

alpha-L-iduronidase, beta-D-glucuronidase, and 2-sulfo-L-iduronate 2-sulfatase: preparation and characterization of radioactive substrates from heparin

Radioactive disaccharide substrates for alpha-L-iduronidase, beta-D-glucuronidase, and 2-sulfo-L-iduronate 2-sulfatase have been prepared from heparin by deaminative cleavage followed by reduction with NaBT4. Six disaccharides were isolated from this reaction mixture and identified. Acid hydrolysis of the major disaccharide, O-(alpha-L-idopyranosyluronic acid 2-sulfate)-(1 linked to 4)-(2,5-anhydro-D-mannitol-l-t 6-sulfate (IdAs--Ms), produced 48% of O-(alpha-L-idopyranosyluronic acid)-(1 linked to 4)-(2,5-anhydro-D-mannitol-l-t 6-sulfate) (IdA--Ms) and 25% of O-(alpha-L-idopyranosyluronic acid)-(1 linked to 4)-2,5-anhydro-D-mannitol-l-t. The most-sensitive substrate for determining alpha-L-iduronidase activity was IdA--Ms which, when incubated with leucocyte and skin-fibroblast homogenates prepared from patients having a deficiency of alpha-L-iduronidase (Mucopolysaccharidosis Type I; MPS-I), was hydrolysed to yield 2,5-anhydro-D-mannitol-l-t 6-sulfate at a rate 50-times less than that found for normal control-preparations. Similarly, O-(beta-D-glucopyranosyluronic acid)-(1 linked to 4)-(2,5-anhydro-D-mannitol-l-t 6-sulfate) was degraded by whole-cell homogenates prepared from beta-D-glucuronidase-deficient (Mucopolysaccharidosis, Type VII) fibroblasts, to yield 2,5-anhydro-D-mannitol-l-t 5-sulfate at a rate 60-times less that that found for MPS-I and normal control-preparations. IdAs--Ms was degraded by 2-sulfo-L-iduronate 2-sulfatase at a rate more than 45-times greater than that found for O-(alpha-L-idopyranosyluronic acid 2-sulfate)-(1 linked to 4)-2,5-anhydro-D-mannitol-l-t. C-6 Sulfation of the anhydro-D-mannitol-l-t residue is an important structural determinant in the mechanism of action of both alpha-L-iduronidase and 2-sulfo-L-iduronate 2-sulfatase on disaccharide substrates.

A substrate for direct measurement of L-iduronic acid 2-sulfate sulfatase

Commercially available sodium heparinate has been sequentially treated with methanolic 0.06M hydrogen chloride and nitrous acid. The nondegraded material was separated by gel filtration from the nonsulfated and monosulfated disaccharides produced. The latter ones, obtained in 10% yield, have been used as a substrate for the direct measurement of the enzyme L-iduronic acid 2-sulfate sulfatase present in human plasma and fibroblast homogenates. Studies of the kinetics and pH optimum of the enzyme, by use of plasma of a patient with mucolipidosis II, indicated an apparent Km of 2.5mM and a pH optimum of 4.6--4.8. The levels of activity in normal plasma and plasma of a patient with Hunter's disease were found to be 20.4 +/- 1.22 units (mumol sulfate/24 h/g protein) and 3.25 +/- 0.35 units, respectively. In homogenates of cultured skin fibroblasts, the levels were 137.6 +/- 10.7 units for normal controls and 6.4 +/- 5.1 for patients with Hunter's disease. The plasma two obligated heterozygotes gave intermediate levels of activity, whereas the plasma of two possible heterozygotes gave either intermediate levels or entirely normal levels of activity.

A radioactive substrate and assay for alpha-L-iduronidase

A novel radioactive substrate for alpha-L-iduronidase, anhydro[3H]mannitol-iduronide has been prepared. This compound is hydrolysed by alpha-L-iduronidase to yield anhydro[3H]mannitol, which can be separated from the substrate and counted. The assay, described for use with fibroblast homogenates, is satisfactory for the diagnosis of mucopolysaccharidosis I.

Mosaicism for sulfoiduronate sulfatase deficiency in carriers of Hunter's syndrome

Using an assay for sulfoiduronate sulfatase based on the degradation of 35S mucopolysaccharides in a cell-free system, two clonal populations have been demonstrated in fibroblasts of heterozygotes for Hunter's syndrome. The locus responsible for sulfoiduronate sulfatase deficiency in this X-linked mucopolysaccharidosis is therefore subjected to dosage compensation in females.

The mucopolysaccharidoses (a review)

The mucopolysaccharidoses are a group of genetic diseases characterized by storage of incompletely degraded glycosaminoglycans. Such storage causes marked distortion of many tissues with consequent severe somatic changes and mental retardation. Storage of glycosaminoglycans results from markedly diminished activity of specific hydrolases requisite for the normal degradation of glycosaminoglycans. The specific enzymic defects have been identified in nine different diseases. In some cases evidence has been obtained indicating the existence of additional allelic diseases based on the same enzyme. The knowledge obtained from these studies has made prenatal diagnosis possible and has led to the possibility that therapy may be undertaken utilizing enzyme replacement.