L-Aspartate-induced activation of aspartase.
During the catalysis of the fumarate amination reaction, aspartase was markedly activated by the product, L-aspartate, as shown by a steep increase in the reaction rate. When NH4+ was replaced by NH2OH, the hydroxylamination reaction proceeded without any acceleration, and was activated upon addition of L-aspartate. The activation required the Mg2+ ion and the alkaline pH, and the half-saturation concentration of L-aspartate for activation was as low as 0.07 mM, which was far lower than the Km value for catalysis. Fumarate showed no activating effect in contrast to L-aspartate, and L-aspartate lowered the Km value for fumarate instead of acting as a competitive inhibitor. Besides L-aspartate, alpha-methyl-DL-aspartate exhibited an activating effect without serving as a substrate. These results suggest that the activation is mediated by an indirect action of L-aspartate which is bound to a site distinct from the catalytic site.
D000642:Ammonia-Lyases / Q000378:metabolism*; D001220:Aspartate Ammonia-Lyase / Q000378:metabolism*; D001224:Aspartic Acid / Q000378:metabolism*; D004789:Enzyme Activation; D004926:Escherichia coli / Q000201:enzymology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D013056:Spectrophotometry, Ultraviolet
D001224:Aspartic Acid; D000642:Ammonia-Lyases; D001220:Aspartate Ammonia-Lyase