In enzymology, fructuronate reductase () is an enzyme that catalyzes the chemical reaction
The two substrates of this enzyme are D-mannonic acid and oxidised nicotinamide adenine dinucleotide (NAD<sup>+</sup>). Its products are D-fructuronic acid (shown in its keto form), reduced NADH, and a proton.
This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-OH group of donor with NAD<sup>+</sup> or NADP<sup>+</sup> as acceptor. The systematic name of this enzyme class is D-mannonate:NAD<sup>+</sup> 5-oxidoreductase. Other names in common use include mannonate oxidoreductase, mannonic dehydrogenase, D-mannonate dehydrogenase, and D-mannonate:NAD<sup>+</sup> oxidoreductase. This enzyme participates in pentose and glucuronate interconversions.