EC 2.7.2.4; other name: aspartokinase; an enzyme that catalyses the formation of 4-phospho-l-aspartate from ATP and l-aspartate with release of ADP. The reaction is the first step in the biosynthesis of lysine, methionine, and threonine in plants and bacteria. In Escherichia coli, the pathway for the synthesis of each amino acid is independently controlled by regulation of isoenzymes specific for each pathway. See homoserine dehydrogenase for another example.