Purification and characterization of L-2,4-diaminobutyrate decarboxylase from Acinetobacter calcoaceticus

Acinetobacter calcoaceticus ATCC 23055 produces a large amount of 1,3-diaminopropane under normal growth conditions. The enzyme responsible, L-2,4-diaminobutyrate (DABA) decarboxylase (EC 4.1.1.-), was purified to electrophoretic homogeneity from this bacterium. The native enzyme had an M(r) of approximately 108000, with a pI of 5.0, and was a dimer composed of identical or nearly identical subunits with apparent M(r) 53000. The enzyme showed hyperbolic kinetics with a K(m) of 1.59mM for DABA and 14.6μM for pyridoxal 5'-phosphate as a coenzyme. The pH optimum was in the range 8.5-8.75, and Ca²⁺ gave a much higher enzyme activity than Mg²⁺ as a cationic cofactor. N-γ-AcetylDABA, 2,3-diaminopropionic acid, ornithine and lysine were inert as substrates. The enzyme was different in subunit structure, N-terminal amino acid sequence and immunoreactivity from the DABA decarboxylase of Vibrio alginolyticus previously described.