Characterization of Recombinant Human Aromatic l‐Amino Acid Decarboxylase Expressed in COS Cells

Abstract: The expression vector containing the full‐length cDNA of human aromatic l‐Amino acid decarboxylase (EC 4.1.1.28) was transfected in COS cells by a modified calcium phosphate coprecip‐itation method. The cells transfected with plasmids that had a true direction of the cDNA gave a major immunoreactive band at 50 kDa. This expressed enzyme catalyzed the decarboxylation of l‐3,4‐dihydroxyphenylalanine (l‐DOPA). l‐5‐hydroxytryptophan (l‐5‐HTP) and l‐threo‐3,4‐dihydroxyphenylserine. The optimal pH of the enzyme activity with l‐DOPA as a substrate was 6.5, whereas the enzyme had a broad pH optimum when l‐5‐HTP was used as a substrate. Addition of pyridoxal phosphate to the incubation mixture greatly enhanced the activity for both l‐DOPA and l‐5‐HTP.