Determination of phenylethanolamine-N-methyltransferase activity by high-performance liquid chromatography with on-line radiochemical detection.

A new assay technique for phenylethanolamine N-methyltransferase (PNMT) activity by high-performance liquid chromatography with on-line radiochemical detection is described. The method is based on the measurement of 14C-labelled products of the substrate, normetanephrine, using S-adenosyl-L-[methyl-14C]methionine as the methyl donor. The reaction products are determined from the reaction mixture after removal of protein by injecting an aliquot into the liquid chromatograph. The detection limit with 60% counting efficiency is 1.2 pmol of 14C-labelled product. The method is suitable for assaying PNMT activity in the adrenal and in the brain tissue.