5,6-dihydroxy-3-methyl-2-oxo-1,2,5,6-tetrahydroquinoline dehydrogenase  In enzymology, a 5,6-dihydroxy-3-methyl-2-oxo-1,2,5,6-tetrahydroquinoline dehydrogenase () is an enzyme that catalyzes the chemical reaction  Thus, the two substrates of this enzyme are 5,6-dihydroxy-3-methyl-2-oxo-1,2,5,6-tetrahydroquinoline and NAD+, whereas its 3 products are 5,6-dihydroxy-3-methyl-2-oxo-1,2-dihydroquinoline, NADH, and H+. This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-CH group of donor with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is 5,6-dihydroxy-3-methyl-2-oxo-1,2,5,6-tetrahydroquinoline:NAD+ oxidoreductase.