Alternative biosyntheses of meso-diaminopimelate from tetrahydrodipicolinate [8,25]. L-Tetrahydrodipicolinate exists in equilibrium with the enamine product and the acyclic L-2-oxo-6-aminopimelate product [24]. In the succinylate pathway (left), the acyclic form is protected by the tetrahydrodipicolinate N-succinyltransferase enzyme (DapD; EC 2.3.1.117). N-Succinyl-L,L-diaminopimelate aminotransferase (DapC; EC 2.6.1.17) transfers an amino group from L-glutamate, and then N-succinyl-L,L-diaminopimelate desuccinylase (DapE, EC 3.5.1.18) deprotects the product. The L,L-diaminopimelate epimerase enzyme (DapF; EC 5.1.1.7) produces meso-diaminopimelate for lysine and peptidoglycan biosynthesis. Some Gram-positive bacteria use an acetyl protecting group instead of the succinyl group. Alternatively, L,L-diaminopimelate aminotransferase (DapL; EC 2.6.1.83) directly transaminates tetrahydrodipicolinate to produce L,L-diaminopimelate. Finally, some bacteria use a diaminopimelate dehydrogenase enzyme (Ddh; EC 1.4.1.16) to reductively aminate tetrahydrodipicolinate.