Purification and some properties of liver and brain beta-N-acetyl-hexosaminidase S

Does β-hexosaminidase function only as a degranulation indicator in mast cells? The primary role of β-hexosaminidase in mast cell granules

β-Hexosaminidase, which is generally present in the lysosome, is essential for glycoprotein metabolism in the maintenance of cell homeostasis. In mast cells (MCs), large amounts of β-hexosaminidase are present in the granules as opposed to the lysosome, and the biological role of MC β-hexosaminidase has yet to be fully elucidated. Therefore, we investigated the biological role of β-hexosaminidase in MC granules. Bone marrow-derived MCs from C57BL/6 (BL/6-BMMC) or β-hexosaminidase gene-deficient (hexb(-/-)-BMMC) mice were transplanted into MC-deficient (WBB6F1/J-Kit(W)/Kit(W-v) [W/W(v)]) mice to generate MC-reconstituted models. In asthma model experiments, no differences were observed in the symptoms of BL/6, W/W(v), BL/6-BMMC-reconstituted W/W(v), or hexb(-/-)-BMMC-reconstituted W/W(v) mice. In Staphylococcus epidermidis experimental infection model experiments, the severity of symptoms and frequency of death were markedly higher in W/W(v) and hexb(-/-)-BMMC-reconstituted W/W(v) mice than in BL/6 and BL/6-BMMC-reconstituted W/W(v) mice. The growth of S. epidermidis in an in vitro study was clearly inhibited by addition of BL/6-BMMC lysate, but not by addition of hexb(-/-)-BMMC lysate. Moreover, suppression of bacterial proliferation was completely recovered when bacteria were incubated with hexb(-/-)-BMMC lysate plus β-hexosaminidase. Transmission electron microscopy indicated that the cell wall of S. epidermidis was heavily degraded following coincubation of bacteria with BL/6-BMMC lysate, but not following coincubation with hexb(-/-)-BMMC lysate. These findings strongly suggest that MC granule β-hexosaminidase is crucial for defense against bacterial invasion, but is not involved in the allergic response. Our results also suggest that the bactericidal mechanism of β-hexosaminidase involves degradation of bacterial cell wall peptidoglycan.

Beta-N-acetylhexosaminidases A and S have similar sub-cellular distributions in HL-60 cells

In HL-60 cells the most abundant isoenzymes of beta-N-acetyl-hexosaminidase are A (alpha beta) and S (alpha alpha). Sub-cellular fractionation of HL-60 cells by differential centrifugation showed that both A and S forms were present in the lysosomal and post-lysosomal (soluble) fractions in approximately equal abundance. Ion-exchange chromatography showed that a fraction enriched with plasma membranes had the A form, and a form of beta-N-acetylhexosaminidase less acidic than A, but there was no S. Analysis of the alpha-subunits of beta-N-acetylhexosaminidases A and S using Western blotting and immuno-detection with antisera raised to synthetic peptides showed that mature alpha-subunits were present in both A and S isolated from the lysosomal fraction. This observation establishes that the alpha alpha-dimer of beta-N-acetyl-hexosaminidase (S) can be transported to lysosomes in HL-60 cells whereas there is good evidence that this does not take place in fibroblasts. HL-60 cells were not stimulated to secrete lysosomal enzymes by incubating them with NH4Cl and, unlike fibroblasts, are unlikely to use mannose-6-phosphate mediated transport of beta-N-acetylhexosaminidases to lysosomes. Comparison of the sequence of the beta-N-acetylhexosaminidase alpha-subunit with a 43 amino acid sequence of cathepsin D, though to function in the mannose-6-phosphate independent targeting of this enzyme to lysosomes, showed alignment in a region towards the C-terminus in which 21% of the residues were identical with the interposition of a one amino acid gap.

Demonstration and some properties of N-acetyl-beta,D-hexosaminidase (HEX) C isoenzyme in human renal tissues: relative increase of HEX C activity in renal cell carcinoma

The present study has demonstrated the presence of hexosaminidase (HEX) C activity in human renal tissues by an electrophoretic method. At the same time, its enzymatic properties, obtained as unbound fraction of renal tissue extracts passed through a concanavalin A Sepharose column, have been compared with those of HEX A and B. HEX C had the fastest electrophoretic mobility among HEX isoenzymes. The optimal pH of HEX C was 6.5, while that of HEX A and B was 4.9. The Km value of HEX C for synthetic glucosaminide substrate was 1.16 mmol/l, while that of HEX A and B was 0.18 mmol/l and 0.22 mmol/l, respectively. HEX C was inactive for a synthetic galactosaminide substrate, while HEX A and B were active. The percentage of HEX C activity to the total was 7.9 +/- 2.9% and 13.8 +/- 3.0% in the normal and the neoplastic tissues, respectively. A significant difference was observed between them (P < 0.01). These results indicate that the enzymatic properties of HEX C is quite different from those of A and B and also suggest that the determination of HEX C may become one of the useful clinical markers of the human renal cell carcinoma.

Aryl sulphatase isoenzymes of chorionic villi: implications for prenatal diagnosis

Prenatal diagnosis of metachromatic leucodystrophy (MLD) is based on demonstrating a deficiency of aryl sulphatase A (ASA) in the fetus. To evaluate the place of chorionic villus sampling for prenatal diagnosis of this condition, the properties of ASA were compared in chorionic villi and cultured skin fibroblasts. Considerable differences with respect to pH optimum, Km values and linearity with incubation time were found. These differences can be explained by the presence of aryl sulphatase C (ASC), a major component in chorionic villi and placenta. This isoenzyme was shown to have activity towards p-nitrocatechol sulphate (NCS) thereby interfering in the colorimetric assay most often used to detect MLD (Baum et al., 1959)

Synthesis of 4-methylumbelliferyl-beta-D-N-acetylglucosamine-6-sulfate and its use in classification of GM2 gangliosidosis genotypes

Measurement of hexosaminidase A (Hex A) is an important clinical chemical procedure in the classification of GM2 gangliosidosis genotypes. We have synthesized a new substrate which may be useful in both the biochemical diagnosis of GM2 gangliosidosis and the detection of heterozygotes for the Tay-Sachs disease (TSD) allele. 4-Methylumbelliferyl-beta-D-N-acetylglucosamine-6-sulfate (4MUGS) was synthesized by sulfation of 4MU-beta-D-N-acetylglucosamine (4MUG) with chlorosulfonic acid and purified through gel filtration and ion-exchange chromatography. The structure of 4MUGS was verified by elemental analysis and NMR. Hex A is approximately 100 times more active toward 4MUGS than Hex B. The advantage of this increased specificity is that Hex A can be determined in a one-step procedure which allows separation of normal control serum values from those of obligate heterozygotes. Alternatively, assay values obtained using both substrates can be transformed by application of an empirical equation that allows the calculation of both Hex A and Hex B without the requirement of thermal fractionation. Lower values for % Hex A in serum have been obtained for Tay-Sachs homozygotes using the 4MUGS assay procedure. The results of Hex A assays on fibroblast cell strains obtained from Tay-Sachs homozygotes, variant forms of GM2 gangliosidosis and normal controls are also discussed.

Demonstration of the existence, and partial characterization, of a cell-surface beta-hexosaminidase from rat splenocytes

Rat splenocytes are shown to exhibit cell-surface located beta-N-acetylglucosaminidase and beta-galactosidase activities. Preincubation experiments, solubilization experiments and chemical cross-linking experiments show that these enzymatic activities are indeed cell-surface localized. The solubilization and partial purification of the beta-N-acetylglucosaminidase activity is reported. Kinetic studies of the partially purified material with a variety of competitive inhibitors at several pH values suggest that at physiological pH the cell surface beta-N-acetylglucosaminidase may function as a carbohydrate binding protein rather than as a glycosidase.