Purification and characterization of galactocerebroside sulfotransferase from rat kidney

Abstract

Galactocerebroside sulfotransferase (EC 2.8.2.11) was purified to apparent homogeneity from rat kidneys. The purified protein is stable at −20 °C, and has an estimated molecular weight of 64,000 and a pI of 5.1. In contrast to other known sulfotransferases, the enzyme appears not to require divalent metal ions for activity. The K m for the donor, 3′-phosphoadenosine 5′-phosphosulfate, is 5.2 μ m. Structural studies on this “active” sulfate donor show the requirement of a phosphate group at the 3′ position of the ribose moiety. Modification of the amino group at either the 6 or 8 position on the purine ring renders the corresponding compounds poor substrates. Both galactosylceramide and lactosylceramide are effective acceptors for this enzyme, while galactosylsphingosine and galactosylglycerolipids are sulfated only poorly, suggesting that the in vivo sulfation of these glycolipids is carried out by different sulfotransferases. The active site of the enzyme contains arginine residues which appear to be important in binding the sulfate donor. The enzyme protein is hydrophobic and binds 0.17 mg [ 3H]Triton X-100/mg protein. The purified enzyme contains bound lipids, consisting primarily of cholesterol and phosphatidylcholine. The lipid environment affects the activity of the enzyme which, in turn, regulates the sulfation of glycolipids.