Arylsulfohydrolase kinetic properties

The removal of neuraminyl residues from pure arylsulfohydrolase A by bacterial neuraminidase does not alter the specific activity, kinetic properties, and general stability but does change the elution profile through a DEAE-cellulose column (Fig. 1) and the electrophoretic mobility on a polyacrylamide gel (Graham and Roy, 1973 Farooqui and Srivastava, 1979). Das and Bishayee (1980) claimed that the treatment of partially purified sheep brain arylsulfohydrolase A with bacterial neuraminidase did not cause a... 

Arylsulfohydrolase A forms an enzymatically active insoluble complex with a plant lectin, concanavalin A (Con A), at a high salt concentration, where electrostatic interactions are minimal (Bishayee et al., 1973 Bishayee and Bachhawat, 1974 Farooqui and Srivastava, 1981). This insoluble complex can be isolated by centrifugation. Con A-immobilized enzyme has greater thermostability (Ahmad et al., 1973 Farooqui and Srivastava, 1981) and displays a broad pH optimum between pH 3.5 and 4.5. Immobilization on Con A also induces changes in the affinity of substrate with arylsulfohydrolase A. The kinetic properties of free and immobilized arylsulfohydrolase A are shown in Table 3. 

Lakshmi and Balasubramanian (1980) showed the presence of a new multiple form of arylsulfohydrolase B in human and monkey brain. Arylsulfohydrolase B, can be separated by DEAE-cellulose chromatography (Mathew and Balasubramanian, 1984). The B, form totally binds to Sephadex G-200 and was not eluted with 1.0 M NaCl, 0.5 M glucose, 0.5 M glucose plus 0.5 M NaCl, 0.5 M KSCN, 1 M urea, or 1% Triton X-100. The treatment of arylsulfohydrolase B with Escherichia coli alkaline phosphatase results in the formation of a less acidic form, presumably due to dephosphorylation. The dephosphorylated form does not bind to DEAE-cellulose. Inorganic phosphate and serine phosphate but not mannose 6-phosphate can inhibit this dephosphorylation. The kinetic properties of the phosphorylated and dephosphorylated arylsulfohydrolase are quite similar. The possibility that arylsulfohydrolase B is a dephosphorylated form of B, has been ruled out by the significant differences between substrate concentration and activity curves of these enzymes. 

The kinetic properties of these multiple forms are quite similar (Farooqui, 1976b). With p-nitrocatechol sulfate as substrate, arylsulfohydrolase B has a value at least three times higher than that of arylsulfohydrolase A. Sulfate ions produce a noncompetitive inhibition of this enzyme with a K value of... 

Several cases of a new form of metachromatic leukodystrophy have been reported (Hahn et al., 1981, 1982 Inui et al., 1983). These cases have clinical symptoms resembling juvenile metachromatic leukodystrophy, but have only about half of the normal arylsulfohydrolase A activity in leukocytes and fibroblasts. The kinetic properties of the arylsulfohydrolase A from fibroblasts are normal. However, the cerebroside 3-sulfate loading test (Porter et al., 1971a) with growing fibroblasts shows an abnormal response, indicating a disturbance in arylsulfatase A activity. Supplementation with the activator (Stevens et al., 1981) of arylsulfatase A results in a normal cerebroside 3-sulfate loading test. This indicates that the new form of metachromatic leukodystrophy is not caused by the deficiency of arylsulfohydrolase A, but rather is caused by a deficiency of the activator protein (Shapiro et al., 1979). Fujibayashi and Wenger (1986) have studied the biosynthesis of sulfa-tide/GMj activator protein in control and mutant cultured skin fibroblasts. Their results indicate that patients with variant form of metachromatic leu-... 

---