Catalyzes the stereoinversion of LL-2,6-diaminoheptanedioate (L,L-DAP) to meso-diaminoheptanedioate (meso-DAP), a precursor of L-lysine and an essential component of the bacterial peptidoglycan. (2S,6S)-2,6-diaminoheptanedioate = meso-2,6-diaminoheptanedioate Inhibited by sulphydryl alkylating agents, 2-nitro-5-thiocyanatobenzoate (NTCB), 5,50-dithiobis(2-nitrobenzoic acid) (DTNB) and 1,2-benzisothiazolidine 3-one (BIT) at nanomolar concentrations. kcat is 0.1465 sec(-1) for epimerase activity. Optimum pH is 7.5. DapF is almost 50% more active at 30 degrees Celsius than at 25 degrees Celsius. At 37 degrees Celsius the activity is slightly less than at 30 degrees Celsius. Amino-acid biosynthesis; L-lysine biosynthesis via DAP pathway; DL-2,6-diaminopimelate from LL-2,6-diaminopimelate: step 1/1. Was identified as a high-confidence drug target. Belongs to the diaminopimelate epimerase family.