In enzymology, a saccharopine dehydrogenase (NAD+, L-lysine-forming) (EC 1.5.1.7) is an enzyme that catalyzes the chemical reaction

N₆-(L-1,3-dicarboxypropyl)-L-lysine + NAD⁺ + H₂O ${\displaystyle \rightleftharpoons }$ L-lysine + 2-oxoglutarate + NADH + H⁺

The 3 substrates of this enzyme are N6-(L-1,3-dicarboxypropyl)-L-lysine, NAD⁺, and H₂O, whereas its 4 products are L-lysine, 2-oxoglutarate, NADH, and H⁺.

This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-NH group of donors with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is N6-(L-1,3-dicarboxypropyl)-L-lysine:NAD+ oxidoreductase (L-lysine-forming). Other names in common use include lysine-2-oxoglutarate reductase, dehydrogenase, saccharopine (nicotinamide adenine dinucleotide,, lysine forming), epsilon-N-(L-glutaryl-2)-L-lysine:NAD oxidoreductase (L-lysine, forming), N6-(glutar-2-yl)-L-lysine:NAD oxidoreductase (L-lysine-forming), 6-N-(L-1,3-dicarboxypropyl)-L-lysine:NAD+ oxidoreductase, and (L-lysine-forming). This enzyme participates in lysine biosynthesis and lysine degradation.

As of late 2007, only one structure has been solved for this class of enzymes, with the PDB accession code 1FF9.