Physical characterization of a monoamine-sulfating form of phenol sulfotransferase from human platelets

The purification to homogeneity and physical characterization of a monoamine-sulfating form of phenol sulfotransferase (PST) from human platelets is described. DEAE-cellulose chromatography of a 100,000 x g supernatant solution of homogenized human platelets revealed the presence of two peaks of both dopamine- and phenol-sulfating activity, termed M- and P-PST, respectively. The latter dopamine-sulfating form eluting from the ion exchange column, M(II)-PST, was purified approximately 10,000-fold to electrophoretic homogeneity by Sephacryl S-200 HR and 3'-phosphoadenosine-5'-phosphate-agarose chromatography. The final specific activity of the enzyme was 930 nmol/min/mg of protein. As determined by the hydrodynamic properties of M(II)-PST, the native M(r) was approximately 69,000. The frictional ratio (f/f(o)) was estimated to be 1.28, indicating that the enzyme possesses a relatively low degree of asymmetry. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of the affinity-purified enzyme revealed the presence of single M(r) species of approximately 34,000, suggesting that M(II)-PST exists as a homodimer in vivo. Isoelectric focusing of purified M(II)-PST yielded a single protein species with a pI of 4.7. The sulfhydryl-modifying reagent N-ethylmaleimide (50 μM) was found to inactivate M(II)-PST in a time-dependent manner. This inactivation was totally prevented by saturating concentrations of 3'-phosphoadenosine-5'-phosphosulfate, whereas dopamine bestowed only partial protection to the enzyme. These results suggest that at least one sulfhydryl moiety is present at the active site of M(II)-PST.