The substrate of the enzyme was initially thought to be (S)-2,3-dihydrodipicolinate [1], and the enzyme was classified accordingly as EC 1.3.1.26, dihydrodipicolinate reductase. Later studies of the enzyme from the bacterium Escherichia coli have suggested that the actual substrate of the enzyme is (2S,4S)-4-hydroxy-2,3,4,5-tetrahydrodipicolinate, and that its activity includes a dehydration step [2], and thus the enzyme has been reclassified as 4-hydroxy-tetrahydrodipicolinate reductase. However, the identity of the substrate is still controversial, as more recently it has been suggested that it may be (S)-2,3-dihydrodipicolinate after all [3].
