“…In many of these organisms at least one of these enzymes is bifunctional, catalyzing both the ®rst reaction, the phosphorylation of aspartate and, surprisingly, the third reaction, the reduction of aspartate semialdehyde to homoserine, in this metabolic sequence. In E. coli there are three aspartokinases, two of which are bifunctional enzymes; the other, aspartokinase III (AK III), is a monofunctional enzyme inhibited by high lysine levels (Cohen & Dautry-Varsat, 1980). The sequence of the AK III catalytic domain has 44% homology to the bifunctional aspartokinase domains.…”