Assay for tyrosine hydroxylase by high-performance liquid chromatography with fluorescence detection

A sensitive assay method for tyrosine hydroxylase in rat brain and adrenal medulla by high-performance liquid chromatography with fluorescence detection is described. L-DOPA formed enzymatically from the substrate L-tyrosine and alpha-methyldopa (internal standard), after clean-up with small cartridges of an activated alumina and a cation exchanger, Toyopak IC-SP M, are converted into the corresponding fluorescent compounds by reaction with 1,2-diphenylethylenediamine. The derivatives are separated by reversed-phase chromatography on TSK gel ODS-120T. The detection limit for L-DOPA formed enzymatically is 2 pmol per assay tube.