Microradioisotopic assay for indoleamine N-methyltransferase and analysis of products by liquid chromatography

A rapid method for the separation of tryptamine, 5-hydroxytryptamine, and their N-methylated derivatives is described. The method involves liquid chromatography using a cation exchange column with the eluant monitored either by ultraviolet or fluorescence spectroscopy. The latter technique permits the detection of picogram quantities of indoleamines. Using normal-phase liquid chromatography a complete separation of tryptamine, its N-methylated derivatives, and their β-carboline analogs was also achieved. A radioisotopic assay with the potential to detect indoleamine N-methyltransferase activity in milligram quantities of rabbit lung tissue was developed. The radioisotopically labeled products formed from a number of substrates in such assays were characterized by liquid chromatography.