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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 pl 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 1.59 mM for DABA and 14.6 μM 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-AcetyIDABA, 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.
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