In enzymology, a saccharopine dehydrogenase (NADP+, L-lysine-forming) (EC 1.5.1.8) is an enzyme that catalyzes the chemical reaction

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

The 3 substrates of this enzyme are N6-(L-1,3-dicarboxypropyl)-L-lysine, NADP⁺, and H₂O, whereas its 4 products are L-lysine, 2-oxoglutarate, NADPH, 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:NADP+ oxidoreductase (L-lysine-forming). Other names in common use include lysine-2-oxoglutarate reductase, lysine-ketoglutarate reductase, L-lysine-alpha-ketoglutarate reductase, lysine:alpha-ketoglutarate:TPNH oxidoreductase, (epsilon-N-[gultaryl-2]-L-lysine forming), saccharopine (nicotinamide adenine dinucleotide phosphate,, lysine-forming) dehydrogenase, 6-N-(L-1,3-dicarboxypropyl)-L-lysine:NADP+ oxidoreductase, and (L-lysine-forming). This enzyme participates in lysine biosynthesis and lysine degradation.