Protein sulfotransferase (S) in soluble fraction of rat bran were characterized using [^(35)S] phosphoadenosinephosphosulfate (PAPS) as sulfate donor. [^(35)S] PAPS, the universal sulfate donor, was prepared enzymatically in rat liver high speed supernatant with carrier free ^(35)S0₄ and ATP. The activity of soluble protein sulfotransferase was observed in assay system containing [^(35)S] PAPS, Tris-maleate buffer pH 6.7 and soluble proteins from rate brain. The sulfated proteins were separated by SDS-PAGE and acid treatment was performed on the gel to differentiate tyrosine sulfate from carbohydrate sulfate. Incorporation of sulfate into tyrosine residues of proteins of various molecular weights was observed. Particularly high molecular weight ($gt;200 kD) proteins were more intensively sulfated.
Effects of incubation time, temperature, pH, amounts of proteins, PAPS concentration, various metal ions, and some polyamino acids on the activities of protein sulfotransferases were investigated. These general properties of the soluble sulfotransferase were mostly distinct from those of the microsome associated sulfotransferase.