Comparative activity of arylsulphatases A and B on two synthetic substrates

Emerging Approaches for Fluorescence-Based Newborn Screening of Mucopolysaccharidoses

Interest in newborn screening for mucopolysaccharidoses (MPS) is growing, due in part to ongoing efforts to develop new therapies for these disorders and new screening assays to identify increased risk for the individual MPSs on the basis of deficiency in the cognate enzyme. Existing tests for MPSs utilize either fluorescence or mass spectrometry detection methods to measure biomarkers of disease (e.g., enzyme function or glycosaminoglycans) using either urine or dried blood spot (DBS) samples. There are currently two approaches to fluorescence-based enzyme function assays from DBS: (1) manual reaction mixing, incubation, and termination followed by detection on a microtiter plate reader; and (2) miniaturized automation of these same assay steps using digital microfluidics technology. This article describes the origins of laboratory assays for enzyme activity measurement, the maturation and clinical application of fluorescent enzyme assays for MPS newborn screening, and considerations for future expansion of the technology.

Transport, binding, and metabolism of sulfate conjugates in the liver

Sulfate conjugates are a heterogeneous class of polar, anionic metabolites that result from the conjugation of endogenous and exogenous compounds. Sulfate conjugates exhibit a high degree of binding to albumin, the extent of which usually exceeds those of their parent compounds. Preponderant direct and indirect evidence suggests that sulfation activity is slightly higher in the periportal than in the perivenous (centrilobular) region of the liver, but recent immunohistochemical studies imply that specific isoforms of the sulfotransferases may also be preferentially localized in the perivenous region. Entry of sulfate conjugates into the liver cell is poor unless discrete carriers are present. Although known transport carriers exist for the sulfated bile acids, the specificity of the carriers for drug sulfate conjugates is presently unknown. The removal of sulfates is usually by way of biliary excretion while, on occasion, sulfates can be desulfated and participate in futile cycling with their parent compounds. The binding, transport, and hepatic elimination of various drug sulfate conjugates are examined. Non-recirculating studies carried out in the perfused rat liver with the multiple indicator dilution technique under varying input sulfate conjugate concentrations have provided essential information on the effects of vascular (red blood cells and plasma protein) binding on transport and removal of the conjugates. These studies clearly demonstrate the need to study protein binding, transmembrane transfer characteristics across the liver basolateral (sinusoidal) and canalicular membranes, and enzyme zonation in a distributed-in-space fashion in order to properly define the handling of sulfate conjugates in the liver.

Analysis of N-acetylgalactosamine-4-sulfatase protein and kinetics in mucopolysaccharidosis type VI patients

A sensitive and specific, monoclonal antibody-based immunoquantification assay has facilitated determination of the N-acetylgalactosamine-4-sulfatase (4-sulfatase) protein content in cultured fibroblasts from normal controls and mucopolysaccharidosis type VI (MPS VI) patients. The assay enabled the quantification of 4-sulfatase protein by using a panel of seven monoclonal antibodies and has shown that fibroblasts from 16 MPS VI patients contained less than or equal to 5% of the level determined for normal controls. Fibroblasts from the most severely affected patients contained the lowest levels of 4-sulfatase protein, usually with few epitopes detected, while fibroblasts from mildly affected patients had higher levels of 4-sulfatase protein, with all seven epitopes detected. The pattern of epitope expression is proposed to reflect the conformational changes in the 4-sulfatase protein that arise from different mutations in the 4-sulfatase gene. Immunoquantification in combination with a specific and highly sensitive 4-sulfated trisaccharide-based assay of enzyme activity in these MPS VI patient fibroblasts enabled the determination of residual 4-sulfatase catalytic efficiency (kcat/Km). The capacity of fibroblasts to degrade substrate (catalytic capacity) was calculated as the product of 4-sulfatase catalytic efficiency and the content of 4-sulfatase in fibroblasts. One patient, 2357, with no clinical signs of MPS VI but with reduced 4-sulfatase activity and protein (both 5% of normal) and dermatansulfaturia, had 5% of normal catalytic capacity. The other 15 MPS VI patient fibroblasts had 0%-1.4% of the catalytic capacity of fibroblasts from normal controls and were representative of the spectrum of MPS VI clinical phenotypes, from severe to mild.(ABSTRACT TRUNCATED AT 250 WORDS)

A specific fluorogenic assay for N-acetylgalactosamine-4-sulphatase activity using immunoadsorption

A method combining immune capture and enzyme detection by fluorochemistry has been developed for the diagnostic assay of N-acetylgalactosamine-4-sulphatase (4-sulphatase). The procedure uses a monoclonal antibody 4-S 4.1 to immunoadsorb 4-sulphatase specifically from complex protein samples containing other sulphatases, and 4-methylumbelliferyl sulphate to detect captured 4-sulphatase. The assay provides an accurate and simple method for the diagnosis of Maroteaux-Lamy syndrome (Mucopolysaccharidosis type VI).

Mammalian arylsulfatases A and B: relative rates of hydrolysis of artificial substrates

Rodent and bovine arylsulfatase B hydrolyze 4-methylumbelliferyl sulfate (4MUS) 10- to 30-fold more efficiently than arylsulfatase A. Therefore, 4MUS grossly underestimates arylsulfatase A activity in the presence of excess arylsulfatase B.

Comparative studies of rodent anionic arylsulfatases

Approximately 25 and 40%, respectively, of murine (Mus musculus) and rat (Rattus norvegicus) hepatic arylsulfatase (EC 3.1.6.1) activity eluted from DEAE-ion exchange resins under high salt conditions. This high salt fraction contained arylsulfatase A and an enzyme which was immunologically similar to arylsulfatase B. The latter enzyme was thermostable, resistant to inhibition by silver, completely inhibited by phosphate, displayed linear kinetics, and had a higher pH optimum than arylsulfatase A. Anionic arylsulfatase B also hydrolyzed chondroitin-4-SO4 heptasaccharide. Sephacryl S-300 gel filtration resolved anionic arylsulfatase B into 55 and 115 kd fractions. Rodent arylsulfatase A activity was grossly underestimated when 4-methyl-umbelliferyl sulfate was employed as substrate.

Basic findings and current developments in sphingolipidoses

Sphingolipidoses are caused by recessively inherited deficiencies of lysosomal hydrolases. The clinical backgrounds of and current biochemical and genetic approaches to the different forms and variants of gangliosidoses, trihexosylceramidosis (Fabry's disease), galactosylceramidosis (Krabbe's disease), sulfatidoses (metachromatic leukodystrophies), glucosylceramidosis (Gaucher's disease), sphingomyelinoses (Niemann-Pick disease) and ceramidosis (Farber's disease) are presented.

Plasma acid hydrolases in normal adults and children, and in patients with some lysosomal storage diseases

Optimal assay conditions are described for plasma alpha-galactosidase, beta-glactosidase, beta-glucuronidase, alpha-mannosidase, alpha-glucosidase, N-acetyl-beta-glucosaminidase, alpha-fucosidase, N-acetyl-alpha-glucosaminidase, acid phosphatase and arylsulphatase A. The levels of these activities in normal adults and children, and the stabilities of the activities on storage at -20 degrees C or 4 degrees C, are reported. The levels of these enzymic activities in plasma from patients with Fabry, Pompe, Sanfilippo A, Sanfilippo B, Tay Sachs and Hunter diseases, GM1-gangliosidosis and metachromatic leucodystrophy are described, and the possibility of using plasma hydrolase activities in the diagnosis of these conditions is discussed.

Comparative activity of sulphatases in human liver on two synthetic substrates

Ion-exchange chromatography and gel chromatography manifested the presence of three different forms of sulphatase activity in human liver using 4-methylumbelliferyl sulphate as substrate. Studies with the substrate 4-nitrocatechol sulphate and inhibition experiments with AgNO3 were also performed on these three different forms of sulphatases. This makes it possible to identify the three forms as arylsulphatase A, B, and C. The conclusion is drawn that the 4-methylumbelliferyl sulphate substrate is inadequate to measure the lysosomal arylsulphatases A and B, but it could be used to measure the microsomal arylsulphatase C.

A sensitive fluorescence assay for the simultaneous and separate determination of arylsulphatases A and B

A sensitive fluorometric assay utilizing 4-methylumbelliferyl sulphate has been developed for the simultaneous determination of arylsulphatases A and B from leucocytes, based on the differential effect of silver ions on the two enzymes. The procedure allows discrimination between normal cases and those with metachromatic leucodystrophy.