L-homoserine + NADP(+) = H(+) + L-aspartate 4-semialdehyde + NADPH L-homoserine + NAD(+) = H(+) + L-aspartate 4-semialdehyde + NADH ATP + L-aspartate = 4-phospho-L-aspartate + ADP Threonine interaction with Gln-443 leads to inhibition of aspartate kinase activity and facilitates the binding of a second threonine on Gln-524, leading to a partial inhibition of homoserine dehydrogenase activity (25% of activity remaining at saturation with threonine). Homoserine dehydrogenase activity is also partially inhibited by cysteine (15% of activity remaining at saturation with cysteine). No synergy between threonine and cysteine for the inhibition. 13-fold activation of aspartate kinase activity by cysteine, isoleucine, valine, serine and alanine at 2.5 mM and 4-fold activation by leucine at 2.5 mM, but no activation of homoserine dehydrogenase activity. 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-methionine biosynthesis via de novo pathway; L-homoserine from L-aspartate: step 3/3. Amino-acid biosynthesis; L-threonine biosynthesis; L-threonine from L-aspartate: step 1/5. Amino-acid biosynthesis; L-threonine biosynthesis; L-threonine from L-aspartate: step 3/5. Homo- or heterodimer. In the N-terminal section; belongs to the aspartokinase family. In the C-terminal section; belongs to the homoserine dehydrogenase family.