GALACTOCEREBROSIDE SULFOTRANSFERASE: FURTHER CHARACTERIZATION OF THE ENZYME FROM RAT BRAIN

— Myelin has an unusual lipid composition, being particularly rich in sulfatide. This lipid is synthesized by the transfer of sulfate from phosphoadenosine phosphosulfate to galactocerebroside, catalyzed by galactocerebroside sulfotransferase. This paper describes a sensitive assay for the sulfotransferase (capable of measuring activity in as little as 10 μg of extracted rat brain protein) so that this enzyme can be readily investigated in isolated cells, or the small amounts of tissue available in developing animals. Both manganase (20 mm) and thiol reagents were required for optimal activity. This assay was used to monitor the purification of the sulfotransferase from rat brain. Extraction of the enzyme from crude homogenates required the nonionic detergent, Triton X-100, at pH 7–7.5. Removal of Triton X-100 from the extracted enzyme resulted in a soluble but less active enzyme, the activity of which could then be restored with detergents. Stability of the detergent-extracted enzyme was investigated, and even at —40°C there was a 20% loss of activity over 10 days. By standard procedures 500-fold purification of the enzyme has been achieved.