Purification and properties of an arylsulphatase from the digestive gland of Haliotis iris

Abstract

1. 1. Arylsulphatase (EC 3.1.6.1) from the digestive gland of Haliotis iris exists in multiple forms of different isoelectric point which have activity with both nitrocatechol sulphate and ascorbic acid-2-sulphate. 2. 2. An additional enzyme form, possessing activity with only nitrocatechol sulphate, is also present in crude homogenates. 3. 3. The principal form of the enzyme, isoelectric at pH 5.0, has been purified to near homogeneity by a procedure involving acid precipitation, ammonium sulphate fractionation, ion exchange chromatography on cellulose phosphate and gel permeation chromatography. 4. 4. The purified enzyme preparation contains two catalytically active proteins of very similar isoelectric point, which show identical pH-activity profiles and are of indistinguishable mol. wt of 65,000. 5. 5. These appear to be functionally identical and, being glycoproteins may be related to other forms of the enzyme by differing in degree of glycosylation. 6. 6. The purified enzyme preparation is active with several sulphated nitrophenols. The most active substrate is nitrocatechol sulphate. This substrate demonstrates marked substrate inhibition at low ionic strength. 7. 7. It is proposed that this inhibition is caused by binding of the substrate to an inhibitory site, which binding is antagonised competitively by high concentrations of buffer anions.