A fluorimetric assay of steroid sulphatase in leukocytes: evidence for two genetically different enzymes with arylsulphatase C activity.

Arylsulphatase C (ASC) activity in leukocytes and fibroblasts measured with 4-methylumbelliferylsulphate, is caused by at least two genetically different sulphatases. One of these is steroid sulphatase (STS). Depending on the substrate concentration, about 10-50% of the ASC activity in leukocytes can be attributed to sulphatases other than STS. Steroid sulphatase can be measured specifically with 4-methylumbelliferylsulphate as the fraction of total ASC activity which is inhibitable by dehydroepiandrosterone sulphate. Using this assay, the adjusted ASC activity in leukocytes from patients with X-linked ichthyosis was 2% of normal. Obligate heterozygotes showed reduced activity.