Assay for aromaticl-amino acid decar☐ylase based on fluorescence derivatization with 1,2-diphenylethylenediamine

Methods based on fluorimetry and high-performance liquid chromatography (h.p.l.c.) for highly sensitive assay of aromaticl-amino acid decar?ylase are described. Dopamine formed enzymatically from a substrate,l-dihydroxyphenylalanine (l-DOPA), after chromatography on a small column of a cation-exchanger, Toyopak SP, is converted to a fluorescent compound by reaction with 1,2-diphenylethylenediamine. The derivative is measured by direct spectrofluorimetry or by reversed-phase h.p.l.c. with fluorimetric detection. The limits of detection for dopamine formed enzymatically in the direct and h.p.l.c. methods are 15 and 1 pmol per assay tube, respectively. The enzyme in rat liver, kidney, brain, heart, adrenal medula and serum can be precisely assayed.