Aromatic L-Amino Acid Decarboxylase from Micrococcus percitreus Purification, Crystallization and Properties

Abstract

An aromatic L-amino acid decarboxylase was crystallized from the cell free extract of Micrococcus percitreus. The purification procedure included protamine sulfate treatment, ammonium sulfate fractionation, DEAE-Sephadex column chromatography and Sephadex G-200 filtration. Crystals were obtained from a solution of the purified enzyme by the addition of ammonium sulfate.
The crystalline enzyme preparation was homogeneous as judged by ultracentrifugation and SDS-polyacrylamide gel electrophoresis. The molecular weight was determined to be approximately 101, 000. The enzyme was evidently composed of two identical subunits of a molecular weight of 48, 000. The enzyme catalyzed the stoichiometric conversion of L-tryptophan to tryptamine and CO₂ in the presence of pyridoxal phosphate. The optimum pH was 9.0 for the conversion.
The Km value and the maximum velocity of L-tryptophan decarboxylation were 2.4 x 10^-3 M and 44 μmol/min/mg of protein, respectively. This enzyme also catalyzed decarboxylation of 5-hydroxy-L-tryptophan, L-phenylalanine, L-tyrosine, 3, 4-dihydroxy-L-phenylalanine, L-kynurenine and their α-methyl amino acid derivatives.