Sulphate conjugation in human liver. Direct measurement of N-acetyldopamine-sulphate.

The overall three-step sulphate conjugating activity of the human liver was determined by the direct measurement of N-acetyldopamine (NADA)-sulphate from ATP and inorganic sulphate. NADA-sulphate was separated from NADA and quantified by HPLC-ECD (high-pressure liquid chromatography-electrochemical detection). The overall sulphate conjugation of NADA showed at pH optimum of 8.0 with apparent Km values for sodium sulphate and NADA of 103 microM and 4.8 microM. respectively. The optimum concentration of ATP was 5 mM and that for Mg2+ ions was 7 mM. The specific activities of 17 samples of human liver, measured by this HPLC-ECD procedure ranged from 940 to 23,128 pmol NADA-sulphate/hr/mg protein. A comparison of these values with those determined by the radiometric method developed previously showed a direct correlation coefficient, r = 0.89. The rates of overall sulphate conjugation of NADA and dopamine measured in these samples by the radiometric assay procedure were also significantly correlated with r = 0.82.