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

Abstract

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 a pH optimum of 8.0 with apparent K m values for sodium sulphate and NADA of 103 μM and 4.8 μM, respectively. The optimum concentration of ATP was 5 mM and that for Mg 2+ ions was 7mM. The specific activities of 17 samples of human liver, measured by this HPLC-ECD procedure ranged from 940 to 23,128 pmol NADA-suphate/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.