Molecular characterization of ST1C1-related human sulfotransferase

Carcinogenic arylamines such as N-hydroxy-2-acetylamino-fluorene (N-OH-AAF) are metabolically activated by mammalian sulfotransferases to form N-hydroxyarylamine O-sulfates. We previously showed that rat ST1C1 efficiently mediate these activations. These reactions occur in liver cytosols of humans as well as rats. However, the enzyme responsible for N-OH-AAF activation has not been identified in humans. In the present study, a human cDNA (ST1C2) encoding a sulfotransferase showing a high similarity with ST1C1, has been isolated from a human fetal liver cDNA library and expressed using a bacterial expression system. A clear difference was observed in the pH optima for p-nitrophenol sulfation between ST1C2 and ST1C1 expressed in Escherichia coli. In addition, ST1C2 did not mediate 3'-phosphoadenosine-5'-phosphosulfate-dependent DNA binding of N-OH-AAF. These results suggest that human ST1C2 has a clear different substrate specificity, in spite of the structural similarity, with rat ST1C1.