Preparation and properties of a homogeneous aromatic l-amino acid decarboxylase from hog kidney

Abstract

Preparations of hog kidney aromatic l-amino acid decarboxylase have been obtained which are 99% pure as indicated by disc gel electrophoresis, sedimentation, and immunological techniques. The purified enzyme has a molecular weight of 112,000 daltons and is associated with about 0.9 mole of tightly bound pyridoxal phosphate. Nevertheless, added pyridoxal phosphate stimulated the activity up to fivefold. The enzyme decarboxylated 3,4-dihydroxyphenylalanine, 5-hydroxytryptophan, tryptophan, phenylalanine, and tyrosine at readily measurable rates. Slow decarboxylation of histidine also occurred. The enzyme was inhibited by sulfhydryl reagents and by certain metal ions, but sulfhydryl compounds and chelating agents had little or no effect. Certain other physical and chemical properties of the enzyme were studied.