Racemase that operates by a 'two-base' mechanism, which involves one active-site cysteine acting as a base to abstract the alpha-proton of an amino acid, while a second cysteine thiol functions as an acid to reprotonate the resulting planar carbanionic intermediate from the opposite face. (2S,6S)-2,6-diaminoheptanedioate = meso-2,6-diaminoheptanedioate Inhibited by aziridino-diaminopimelate (AziDAP). Amino-acid biosynthesis; L-lysine biosynthesis via DAP pathway; DL-2,6-diaminopimelate from LL-2,6-diaminopimelate: step 1/1. This enzyme requires no cofactors. Belongs to the diaminopimelate epimerase family.