Figure 1.

Potential Fates in Bacteria of the Reactive Enamine/Imine Produced by Thr Dehydratase.

Thr dehydratase (IlvA) acts on Thr or Ser to produce an enamine that tautomerizes to an imine. The Ser-derived enamine/imine can react with PLP; the resulting adduct can then react with nucleophilic residue(s) of BCAT (IlvE), inactivating this enzyme. The imine also undergoes hydrolysis to the corresponding 2-oxoacid; this occurs spontaneously but is greatly accelerated by RidA. RidA-mediated hydrolysis thus prevents the enamine/imine from reacting with PLP and inactivating BCAT.

[See online article for color version of this figure.]