Involved in the first step of essential amino acids lysine, threonine, methionine and isoleucine synthesis via the aspartate-family pathway. ATP + L-aspartate = 4-phospho-L-aspartate + ADP Allosterically inhibited by lysine, but not by S-adenosyl-L-methionine (SAM). K(0.5) for lysine in the presence of physiological concentrations of substrates is 7.4 uM. No inhibition by threonine or leucine and no activation or inhibition by alanine, cysteine, isoleucine, serine, valine, methionine, glutamine, asparagine, glutamic acid or arginine. K(cat) is 8.4/sec. Amino-acid biosynthesis; L-lysine biosynthesis via DAP pathway; (S)-tetrahydrodipicolinate from L-aspartate: step 1/4. Amino-acid biosynthesis; L-methionine biosynthesis via de novo pathway; L-homoserine from L-aspartate: step 1/3. Amino-acid biosynthesis; L-threonine biosynthesis; L-threonine from L-aspartate: step 1/5. Highly expressed in xylem of leaves and hypocotyls, stele of roots and in trichomes after bolting. Weak expression in veins and mesophyll cells of caulone leaves, inflorescence stems, sepals, petals and stigmata. Belongs to the aspartokinase family.