Racemases, mechanism-based inactivation

Fig. 4. Simplified mechanism-based irreversible inactivation of alanine racemase by 3-chlorovinylglycine, P = PO -...

Henderson and Johnston [59] based on their work with alanine racemase from B. subtilis proposed catalysis by a single base with motion of the coenzyme-substrate complex in a process they termed a swinging door mechanism (Scheme IX). Their proposed mechanism is based on the observation of pronounced asymmetry in the interaction of many racemases with their enantiomeric substrates [55], for example, in the inactivation of the enzyme by D- and L-/I-chloroalanine [59]. The position of the door relative to the point of protonation/deprotonation would determine whether a D- or an L-amino acid is interacting with the enzyme, and if one position were more stable than the other, the enzyme would interact differently with a D- and an L-isomer. 

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