 Homoserine dehydrogenase catalyzes the reaction of aspartate-semialdehyde (ASA) to homoserine.The overall reaction reduces the C4 carboxylic acid functional group of ASA to a primary alcohol and oxidizes the C1 aldehyde to a carboxylic acid.Residues Glu 208 and Lys 117 are thought to be involved in the active catalytic site of the enzyme.