Conjugation of 4-nitrophenol and 4-hydroxylonazolac in V79-derived cells expressing individual forms of human sulphotransferases

Sulpho conjugation of xenobiotics is catalysed by enzymes of the SULT superfamily. We have studied the conjugation of two model compounds, 4-nitrophenol and 4-hydroxylonazolac, in cultures of V79-derived cell lines that individually express human SULT1A1 (alloenzymes *1 and *V), 1A2 (alloenzymes *1 and *2), 1A3, 1B1, 1E1, 2A1 and rat SULT1E1. 4-Nitrophenol was sulphonated in all recombinant cell lines used but not in the control cell line (V79p). The relative activity in the various cell lines strongly depended on the substrate concentration used (1–1000 μM). 4-Hydroxylonazolac was conjugated in the cell lines expressing the following enzymes, in this order, human SULT1E1>1A1 (*1>*V)>1A2 (*1>*2)>1A3. In all these cell lines, the rate of conjugation increased with the substrate concentration (1–100 μM) without reaching a saturation level. The mass spectrometric and fluorometric analyses used are very sensitive. Preliminary experiments demonstrate that activities can readily be measured in microtitre-plate cultures.