L-Aspartate α-Decarboxylase in a Cell-free System from Escherichia coli

The properties of L-aspartate α-decarboxylase [EC 4.1.1.11] in a crude extract and in a partially purified preparation from E. coli B were studied. 1. Adaptation of the bacteria to substrate by growth in synthetic medium containing 1.5% L-aspartic acid and 0.5% L-glutamic acid before culture in the same medium greatly increased enzyme production. Enzymatic activity increased with bacterial growth to a maximum in the later stage of the logarithmic phase and decreased promptly toward the beginning of the stationary phase, indicating that the enzyme was formed to supply β-alanine required during bacterial growth for biosynthesis of pantothenic acid. Formation of β-alanine from uracil by adapted bacteria was rather slight. 2. The optimum pH of this enzyme was 5.5 and the optimum temperature was rather broad, being 37–47°C. With a partially purified enzyme preparation the Michaelis constant was calculated to be 1.5×10−3M. 3. Pyridoxal 5'-phosphate, α-keto acids and Co2+ and Mg2+ ions activated the enzyme, and their effects were additive. A combination of pyridoxal 5'-phosphate, α-keto-glutaric acid and Co2+ enhanced the enzymatic activity about 13-fold. Cyanide, fluoride, Ag+, Hg2+, semicarbazide, thiourea and isonicotinic acid hydrazide inhibited the decarboxylase.