Purification and Characterization of Aromatic L‐Amino Acid Decarboxylase from Rat Kidney and Monoclonal Antibody to the Enzyme

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Abstract
Aromatic L‐amino acid decarboxylase was purified from rat kidney to homogeneity, as judged by poly‐acrylamide gel electrophoresis, in the presence and absence of sodium dodecyl sulfate (SDS). The final preparation showed an activity of 3,4‐dihydroxyphenylalanine (dopa) decarboxylation of —11,000 nmol/min/mg of protein at 37°C. The purified enzyme also catalyzed the decarboxylation of 5‐hydroxytryptophan, tyrosine, tryptophan, and phenyialanine. The enzyme appeared to be composed of two identical subunits, each possessing a molecular weight of 48,000. The isoelectric point of the enzyme was estimated to be 6.7 in the presence of 8 M urea and 5.60–5.85 in its absence. To examine the identity of aromatic L‐amino acid decarboxylase from various tissues, a monoclonal antibody directed against the enzyme from rat kidney was prepared. Immunotitration and analysis by antibody‐affinity chromatography followed by SDS‐polyacrylamide gel electrophoresis revealed that the enzymes from the stria‐tum, adrenal medulla, pineal gland, liver, and kidney were indistinguishable with respect to immunological cross‐reactivity and molecular size.