The cover illustrates two diastereomers of aziridino-diaminopimelate (azi-DAP), an irreversible inactivator of DAP epimerase (H. influenzae), approaching the monomeric disulfide form of the target enzyme. 

Diaminopimelate (DAP) epimerase is an enzyme which interconverts two diastereoisomers of DAP, namely L,L-DAP and meso-DAP. This process plays an integral part in the synthesis of precursors for the peptidoglycan layer of the bacteria cell wall. Therefore this enzyme is an important target for antibiotics.

In order to develop antibiotics to target this enzyme, we must first understand the mechanism by which the enzyme works. A giant step towards this has been made by John Vederas and co-workers, who have synthesised optically pure aziridine analogues of DAP (azi-DAP). These substrates inhibit DAP epimerase and therefore allow the key active site residues in the enzyme to be identified.

Vederas has also obtained crystal structures of the enzyme with a substrate bound. Analysis of these should lead to a better understanding of the mechanism.