Differential assay of arylsulfatase A and B activities: A sensitive method for cultured human cells

Conventional colorimetric methods for determining arylsulfatase A and B activities are cumbersome and insufficiently sensitive for microassays. A more sensitive fluorogenic technique to determine activities of the two enzymes in human cultured fibroblasts without any prior treatment has been developed. In the assay mixture, lead ions (3 mm) are used to remove endogenous inhibitors and silver ions (0.3 mm) are used to inhibit specifically arylsulfatase A activity. This assay is optimal at pH 5.6 for both enzymes, linear for up to 2 h of incubation at 37° at protein concentrations of 3 to 10 μg for arylsulfatase A and 7 to 40 μg for arylsulfatase B. “Lysis buffer” is the best for extracting arylsulfatase A and 0.15 m sodium acetate for extracting arylsulfatase B. This technique is three- to fivefold more sensitive than the conventional method and applicable to assays of arylsulfatase A or B activity in fibroblasts from patients with various sulfatase deficiencies.