Liberation of N-acetylglucosamine-6-sulfate by human beta-N-acetylhexosaminidase A

The first step of the degradation of p-nitrophenyl-6-sulfo-2-acetamido-2-deoxy-beta-D-glucopyranoside and of keratan sulfate-derived oligosaccharides bearing N-acetylglucosamine-6-sulfate residues at the nonreducing end was considered to be accomplished by the action of a specific sulfatase (Kresse, H., Paschke, E., von Figura, K., Gilberg, W., and Fuchs W. (1980) Proc. Natl. Acad. Sci. U. S. A. 77, 6822-6826). In purification from human placenta, however, this activity co-chromatographed with isoenzyme A of beta-N-acetylhexosaminidase and had the same electrophoretic mobility as the latter enzyme. The activity was precipitated by a specific antiserum against beta-N-acetylhexosaminidase. A pronounced enzyme deficiency was found in Tay-Sachs and Sandhoff fibroblasts. The purified enzyme released p-nitrophenol from the chromogenic substrate as well as a second product which contained equimolar amounts of hexosamine and sulfate. This product had the same electrophoretic and chromatographic behavior as sulfated N-acetylglucosamine. It could be degraded by periodate to a smaller charged fragment. Incubation of keratan sulfate-derived oligosaccharides with beta-N-acetylhexosaminidase A analogously resulted in the liberation of N-acetylglucosamine-6-sulfate. The enzyme showed the highest affinity towards a trisulfated tetrasaccharide and exhibited a similar Km for the sulfated and the unsulfated p-nitrophenyl derivative.

Sulphamidase activity in leucocytes, cultured skin fibroblasts and amniotic cells: diagnosis of the Sanfilippo A syndrome with the use of radiolabelled disaccharide substrate

1. Sulphamidase activity was assayed by incubation of the radiolabelled disaccharide O-(alpha-2-sulphamino-2-deoxy-D-glucopyranosyl)- (1 leads to 3)-L-[6-3H]idonic acid with homogenates of leucocytes and cultured skin fibroblasts and concentrates of urine derived from normal individuals, patients affected with sulphamidase deficiency disorder [mucopolysaccharidosis type IIIA (MPS IIIA): the Sanfilippo A syndrome], parents of such patients and patients affected with other mucopolysaccharidoses and lysosomal enzyme deficiencies. 2. The assay clearly distinguished affected homozygotes from normal controls, heterozygotes and other mucopolysaccharidoses types. 3. Sulphamidase displayed remarkable thermal stability; reaction rates were constant for at least 24 h at 60 degrees C for leucocyte and 20 h at 37 degrees C for cultured fibroblast preparations. Apparent Km values for fibroblast sulphamidase were 71 mumol/l at 37 degrees C and 100 mumol/l at 50 degrees C; the corresponding Vmax, values were 21 and 72 pmol min-1 mg-1 of protein respectively. An incubation temperature of 60 degrees C was used for the routine assay of sulphamidase activity in leucocytes, urine and amniotic supernatant preparations. The specific activities of fibroblast and amniotic cell sulphamidase, assessed at incubation temperatures of 37 degrees C, were more than 10-fold the leucocyte enzyme activity at 60 degrees C. 4. We recommend the use of radiolabelled disaccharide substrate for the assay of sulphamidase in leucocytes, skin fibroblasts and urine, for the routine enzymic detection of the sulphamidase deficiency disorder of the Sanfilippo A syndrome.

The mucopolysaccharidoses: biochemistry and clinical symptoms

The mucopolysaccharidoses are a group of genetic diseases which are characterized by an excessive intralysosomal accumulation of partially degraded mucopolysaccharides. This storage is caused by the inactivity of one of eleven enzymes that are required for the degradation of the different types of mucopolysaccharides. There is a rough correlation between phenotype and chemical nature of the storage material. Similar clinical pictures, however, may be caused by an inactivity of different enzymes. Conversely, different clinical expressions of the defect of a single enzyme may be attributed to allelic mutations. The recent development of specific assay procedures for the respective enzymes allows 1. an early genotype-specific diagnosis of affected patients, 2. prenatal diagnosis of the metabolic defect in families at risk, 3. to prognosticate the course of the disease at least in some instances, and 4. genetic counseling for members of affected families. At present, there is no specific therapy. Attempts of enzyme replacement therapy are still at an experimental stage.

Sanfilippo syndrome type C: assay for acetyl-CoA: alpha-glucosaminide N-acetyltransferase in leukocytes for detection of homozygous and heterozygous individuals

As assay for the detection in leukocytes of homozygous and heterozygous carriers of Sanfilippo syndrome type C is described. In one family with two patients suffering from Sanfilippo C syndrome, the affected individuals had no residual activity to acetyl-CoA: alpha-glucosaminide N-acetyltransferase. The determination of the acetyl-CoA: alpha-glucosaminide N-acetyltransferase/ beta-glucuronidase ratio allows the discrimination between obligate heterozygotes and normal individuals and may be used for carrier detection.

Sanfilippo disease type D: deficiency of N-acetylglucosamine-6-sulfate sulfatase required for heparan sulfate degradation

Skin fibroblasts from two patients who had symptoms of the Sanfilippo syndrome (mucopolysaccharidosis III) accumulated excessive amounts of heparan sulfate and were unable to release sulfate from N-acetylglucosamine-6-sulfate linkages in heparan sulfate-derived oligosaccharides. Keratan sulfate-derived oligosaccharides bearing the same residue at the nonreducing end and p-nitrophenyl-6-sulfo-2-acetamido-2-deoxy-beta-D-glucopyranoside were degraded normally. Kinetic differences between th sulfatase activities of normal fibroblasts were found. These observations suggest that N-acetylglucosamine-6-sulfate sulfatase activities degrading heparan sulfate and keratan sulfate, respectively, can be distinguished. It is the activity directed toward heparan sulfate that is deficient in these patients; we propose that this deficiency causes Sanfilippo disease type D.

Fluorometric measurement of alpha-L-iduronidase activity using 4-methylumbelliferyl-alpha-L-iduronide

Using 4-methylumbelliferyl-alpha-L-iduronide as a substrate, alpha-L-iduronidase activity was measured in leukocytes and in lymphoblastoid cells obtained from patients with alpha-L-iduronidase deficiency and from obligate heterozygotes for this disease. There was complete discrimination between alpha-L-iduronide in leukocytes and in lymphoblastoid cells from the patients and controls. However, overlap was observed between values of the activity in the obligate heterozygotes and those in the controls. 4-Methylumbelliferyl-alpha-L-iduronidase activity because of greater sensitivity, easier assay procedure and shorter incubation period.

A 3H-labelled trisaccharide from heparin as substrate for acetyl-CoA: 2-amino-2-deoxy-alpha-D-glucoside N-acetyltransferase

The tetrasaccharide fraction obtained by gel chromatography after treatment of commercially available heparin with nitrous acid was reduced with NaB3H4 and then hydrolysed with 2M trifluoracetic acid at 70 degrees for 3 days. By gel chromatography and electrophoresis, the 3H-labelled trisaccharide 1 bearing and unsubstituted 2-amino-2-deoxy-D-glucosyl group in the non-reducing position was obtained (18% from the 3H-labelled tetrasaccharide). By sequential, enzymic degradation, the structure alpha-D-GlcN-(1 leads to 4)-beta-D-GlcA-(1 leads to 4)-[1-3H]aManol was obtained for 1, which is a substrate for acetyl-CoA: 2-amino-2-deoxy-alpha-D-glucoside N-acetyltransferase, an enzyme that is deficient in the Sanfilippo C syndrome. In human-skin fibroblasts, the pH optimum of acetyl transfer onto 1 was between pH 5.5 and 7.0, and dependent on the buffer. An apparent Km for 1 of 0.14mM was found.

Acid hydrolases in serum from patients with lysosomal disorders

The activity of acid hydrolases was studied in serum from patients with mucolipidosis (II and III) and other lysosomal disorders. In mucolipidosis II and III all hydrolases examined except alpha-glucosidase, beta-glucosidase and acid phosphatase were greatly increased. High values for beta-galactosidase were seen in mucopolysaccharidosis types I and II, Gaucher's disease, juvenile amaurotic idiocy and metachromatic leucodystrophy. N-Acetyl-beta-glucosaminidase activity was high in mucopolysaccharidosis types I, II, III and Gaucher's disease. The activity of beta-glucuronidase was increased in mucopolysaccharidosis types I, II and III, Gaucher's disease, juvenile amaurotic idiocy and metachromatic leucodystrophy. Acid phosphatase had increased activity only in Gaucher's disease. In several lysosomal storage disorders no increased values could be found. It is suggested that high values in serum from patients with lysosomal storage disorders (not including mucolipidosis II and III) may depend upon liver cell damage, which disturbs the clearing of acid hydrolases from serum.

Alkaline Phosphatase Activity Induction in Human Spleen Sinuses in Storage Diseases

Human splenic sinuses were observed for the induction of alkaline phosphatase (AP) activity in mucopolysaccharidoses of type I and II, in GM1 gangliosidosis, and in Niemann-Pick's disease, type A. A substantially lower degree of activity was found in Sanfillipo's disease, type A, and in hemosiderin pigmentation of the sinuses. In a number of hematological affections and in control spleens AP activity could not be proved by histochemical means. From the formal pathogenetic view, enzyme activity induction is probably related to lysosomal deposition of the material stored.

Is multiple sulphatase deficiency due to defective regulation of sulphohydrolase expression?

Multiple sulphatase deficiency disease is an unusual autosomal recessive disorder characterised biochemically by a deficiency of several sulphohydrolase activities. The laboratory diagnosis of this combined neurological connective tissue disorder is made on the basis of decreased activities of the lysosomal enzymes, arylsulphatase A and arylsulphatase B and the microsomal enzyme, arylsulphatase C. The primary defect in this multi-enzyme deficiency has not been identified. Using immunological techniques to characterise further the residual activities of arylsulphatases A and B in the multiple sulphatase deficiency disease, we have examined the levels of cross-reaching material (CRM) to arylsulphatases A and B in cultured skin fibroblasts from controls and patients with multiple sulphatase deficiency, metachromatic leukodystrophy (deficiency of only arylsulphatase A activity) and Maroteaux-Lamy syndrome (deficiency of only arylsulphatase B activity). We report here results indicating that arylsulphatases A and B in multiple sulphatase deficiency are reduced in their levels of CRM while retaining a normal activity/CRM ratio. Because the two enzymes are apparently structurally unrelated, these data are consistent with the possibility that their combined deficiencies in this disorder may result from a defect in the coordinated expression of sulphohydrolases.

Biochemical discrimination of Hurler and Scheie syndromes

1. Homogenates of cultured skin fibroblasts derived from patients with alpha-L-iduronidase-deficiency disorders (Hurler and Scheie syndromes) were capable of hydrolysing iduronosyl anhydro-[1-3H]mannitol 6-sulphate although at considerably reduced rates compared with normal controls. 2. The Vmax. values of alpha-L-iduronidase from patients with Hurler or Scheie syndromes and from normal controls were 11, 12 and 833 pmol min-1 mg-1 of protein respectively; the corresponding apparent Km values were 656, 50 and 53 mumol/l respectively. The alpha-L-iduronidases from normal and Scheie fibroblast homogenates were shown to exhibit pH optima at 3.6 and 4.1 and were competitively inhibited by both chloride and sulphate ions: Hurler alpha-L-iduronidase activity exhibited the pH optimum at 3.8 and was also inhibited by chloride and to a lesser extent by sulphate ions. 3. The thermal stability of Hurler, Scheie and normal alpha-L-iduronidase activities at 55 degrees C gave half-lives of approximately 1.0, 2.5 and 1.0 h respectively. 4. These biochemical findings clearly demonstrate enzyme differences for these two clinically distinct phenotypes and provide biochemical evidence that the Hurler and Scheie syndromes result from different allelic mutations.

The mucopolysaccaridoses: clinical and biochemical correlations

The mucopolysaccharidoses (MPS) are hereditary diseases that result in deformities related to connective tissues. Some types of MPS lead to progressive mental retardation. Biochemically, these syndromes are characterized by excessive accumulation and excretion of various types of glycosaminoglycans (mucopolysaccharides). These diseases result from absence of various lysosomal enzymes involved in glycosaminoglycan degradation. The definition of the defects in the MPS has led to advancing diagnosis, counseling, and the possibilities of prenatal diagnosis of this group of dieseases.

[Mucolipidosis. biologic characteristics (author's transl)]

Mucolipidosis II is a severe inherited lysosomal storage disease characterized by profound psychomotor retardation, severe Hurler-like skeletal changes and normal urinary mucopolysaccharide excretion. Mucolipidosis II is a related disorder distinguished by its milder course, milder to absent mental retardation and survival to adult life. Cultivated fibroblasts from patients with both of these disorders display large inclusions on phase microscopy and reduced levels of many acid hydrolases. However, culture medium fibroblasts out the body fluids of affected patients show enormously elevated levels of these hydrolases. The lysosomal enzyme activities in serum, leukocytes, fibroblasts extracts and culture medium from seven patients with mucolipidosis II are similar to those found in four cases of mucolipidosis III. The findings of excessive excretion of sialyl-oligosaccharide in urine and of increased level of sialic acid compounds in cultured fibroblasts associated with a sialidase deficiency in leukocytes, fibroblasts and serum are discussed.

Arylsulphatases A and B in human diploid fibroblasts: differential assay with 4-methylumbelliferylsulphate and AgNO3

A new technique is introduced for the differential assay of arylsulphatases A and B in centrifuged homogenates of cultured human skin fibroblasts, using 4-methylumbelliferyl-sulphate as a substrate and AgNO3 as a selective inhibitor of arylsulphatase A. The method can be applied in the diagnosis of metachromatic leucodystrophy, mucopolysaccharidosis type VI and mucosulphatidosis. Normal arylsulphatase activities were found in fibroblasts derived from patients with mucopolysaccharidoses types II, III-A and IV, known to be caused by deficiencies of various other sulphatases.

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.

Post- and pre-natal assessment of alpha-L-iduronidase deficiency with a radiolabelled natural substrate

1. α-l-Iduronidase activity was assayed by incubation of iduronosyl anhydro[1-3H]mannitol 6-sulphate with homogenates of cultured skin fibroblasts, amniotic cells and leucocytes derived from normal individuals, patients affected with α-l-iduronidase deficiency disorder (mucopolysaccharidosis type I: Hurler, Scheie and Hurler-Scheie compound) and parents of such patients.

2. The assay for α-l-iduronidase, described for use with these cell types, clearly distinguished affected homozygotes from heterozygotes and normal controls.

3. The mean specific activity of α-l-iduronidase in homogenates prepared from cultured skin fibroblasts and leucocytes from more than seven obligate heterozygotes for mucopolysaccharidosis type I was found to be about one-half of the mean of more than 40 normal controls. A number of heterozygotes had α-l-iduronidase activity that identified them as carriers; others had values clearly within the normal range. Thus heterozygote detection of mucopolysaccharidosis type I is not certain.

4. With iduronosyl anhydro[1-3H]mannitol 6-sulphate used as substrate, cell types from five pregnancies at risk for α-l-iduronidase deficiency were examined; each foetus was predicted to be unaffected. For one foetus it was not possible from measurements of total enzyme activity alone to distinguish between the heterozygous carrier state and affected homozygote. The difficulty was resolved by comparing Michaelis-Menten kinetics of this enzyme in fibroblasts derived from the propositus, mother and normal controls with the kinetics of the enzyme in amniotic cells isolated from the foetus at risk and from normal controls.

Sialidosis: a review of human neuraminidase deficiency

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