Assay for acetyl-CoA:arylamine N-acetyltransferase by high-performance liquid chromatography applied to serotonin N-acetylation.

A specific assay to measure the activity of the enzyme acetyl-CoA:arylamine N-acetyltransferase (EC 2.3.1.5) from pigeon liver is described. The assay is based on the HPLC analysis of N-acetylserotonin formed by the enzymatic reaction. A reversed-phase column (Spherisorb 5-microns ODS 2; 150 x 3.2 mm) eluted with 0.1 M sodium acetate (pH 4.75)/methanol (75:25) permits baseline separation of serotonin and N-acetylserotonin within 5.3 min. Several variables on the enzyme reaction were studied to obtain maximum activity. The enzyme is most active in glycine buffer at pH 9.5. The apparent Km value for serotonin (at 0.6 mM CoASAc) is 0.246 mM and 9.9 microM for CoASAc (at 1.5 mM serotonin). To avoid acetyl-CoA or N-acetylserotonin consumption in side-reactions, the enzyme was purified. A two-step purification process (ammonium sulfate fractionation and affinity chromatography on immobilised amethopterin) yielded 60-70% of the initial enzyme activity with a purification factor of 455-560.