Catalyzes the dehydrogenation of precorrin-2 to form sirohydrochlorin which is used as a precursor in both siroheme biosynthesis and in the anaerobic branch of adenosylcobalamin biosynthesis. NAD(+) + precorrin-2 = 2 H(+) + NADH + sirohydrochlorin Cofactor biosynthesis; adenosylcobalamin biosynthesis; sirohydrochlorin from precorrin-2: step 1/1. Porphyrin-containing compound metabolism; siroheme biosynthesis; sirohydrochlorin from precorrin-2: step 1/1. Up-regulated by sulfur starvation and repressed by cysteine. Also induced by O-acetyl-L-serine (OAS), a direct precursor of cysteine, maybe via inactivation of a putative transcriptional repressor of the cysH operon whose activity is controlled by the intracellular levels of OAS. Cells lacking this gene are unable to grow on minimal medium with nitrate as nitrogen source. Growth is restored only after addition of both cysteine and ammonia to the medium. Belongs to the precorrin-2 dehydrogenase / sirohydrochlorin ferrochelatase family.