Catalyzes the reversible NADPH-dependent reductive amination of L-2-amino-6-oxopimelate, the acyclic form of L-tetrahydrodipicolinate, to generate the meso compound, D,L-2,6-diaminopimelate. Probably plays a role in lysine biosynthesis. Exhibits a high substrate specificity, since alpha-ketoglutarate, pyruvate, oxaloacetate, glyoxylate, alpha-ketobutyrate, alpha-ketovalerate, alpha-ketocaproate, alpha-ketoisocaproate, alpha-ketoisovalerate, and phenylpyruvate are not substrates for the reductive amination reaction, and L,L-2,6-diaminopimelate, D,D-2,6-diaminopimelate, DL-alpha-aminopimelate, meso- and DL-2,5-diaminoadipate, L-djenkolate, L-cystine, L-lysine, S-(beta-aminoethy1)-L-homocysteine, L-ornithine, L-arginine, L-alpha,gamma-diaminobutyrate, L-histidine, L-phenylalanine, L-tyrosine, L-glutamate, L-aspartate, L-leucine, L-valine, L-methionine, L-serine, L-alanine, L-alpha-aminobutyrate, D-lysine, D-glutamate, D-leucine, D-alanine, D-phenylalanine, epsilon-aminocaproate, 7-aminoheptanoate, and 8-aminooctanoate are not substrates for the oxidative deamination reaction. Cannot use NAD(+) or NAD(+) analogs instead of NADP(+) for the oxidative deamination reaction. H2O + meso-2,6-diaminoheptanedioate + NADP(+) = (S)-2-amino-6-oxoheptanedioate + H(+) + NADPH + NH4(+) L,L-2,6-diaminopimelate, D,D-2,6-diaminopimelate and meso-2,5-diaminoadipate competitively inhibit the oxidation of meso-2,6-diaminopimelate. L-2-amino-6-methylene-pimelate is also a potent competitive inhibitor (5 uM) of this reaction. Glyoxylate inhibits the reductive amination of L-2-amino-6-oxopimelate about 30%. The enzyme is inhibited completely by p-chloromercuribenzoate and HgCl(2) in vitro. The rate of the reductive amination reaction is about 11 times higher than that of the oxidative deamination at pH 7.5. Optimum pH is about 10.5 for the oxidative deamination of meso-diaminopimelate and 7.5 for the reductive amination of L-2-amino-6-oxopimelate. The rate of the amination reaction declines markedly above pH 9.0. Amino-acid biosynthesis; L-lysine biosynthesis via DAP pathway; DL-2,6-diaminopimelate from (S)-tetrahydrodipicolinate: step 1/1. Homodimer. Constitutively expressed. Not induced by meso-2,6-diaminopimelate. The reductive amination proceeds through a sequential ordered ternary-binary mechanism. NADPH binds first to the enzyme followed by L-2-amino-6-ketopimelate and ammonia, and the products are released in the order of meso-2,6-diaminopimelate and NADP(+). Moreover, the enzyme is B-stereospecific: the pro-S hydrogen at C-4 of the dihydronicotinamide ring of NADPH is transferred to the substrate. Belongs to the diaminopimelate dehydrogenase family.