In enzymology, precorrin-2 dehydrogenase () is an enzyme that catalyzes the chemical reaction
The two substrates of this enzyme are precorrin-2 and oxidised nicotinamide adenine dinucleotide (NAD<sup>+</sup>). Its products are sirohydrochlorin, reduced NADH, and a proton.
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 precorrin-2:NAD+ oxidoreductase. Other names in common use include Met8p, SirC, and CysG. This enzyme is part of the biosynthetic pathway to cobalamin (vitamin B<sub>12</sub>) in anaerobic bacteria and to Cofactor F430.