In enzymology, a lysine dehydrogenase (EC 1.4.1.15) is an enzyme that catalyzes the chemical reaction

L-lysine + NAD⁺ ${\displaystyle \rightleftharpoons }$ 1,2-didehydropiperidine-2-carboxylate + NH₃ + NADH + H⁺

Thus, the two substrates of this enzyme are L-lysine and NAD⁺, whereas its 4 products are 1,2-didehydropiperidine-2-carboxylate, NH₃, NADH, and H⁺.

This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-NH2 group of donors with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is L-lysine:NAD+ oxidoreductase (deaminating, cyclizing).