mRNA decapping enzyme that specifically removes the nicotinamide adenine dinucleotide (NAD) cap from a subset of mRNAs by hydrolyzing the diphosphate linkage to produce nicotinamide mononucleotide (NMN) and 5' monophosphate mRNA (PubMed:31101919, PubMed:31875550). The NAD-cap is present at the 5'-end of some RNAs; in contrast to the canonical N7 methylguanosine (m7G) cap, the NAD cap promotes mRNA decay (PubMed:31101919). Preferentially acts on NAD-capped transcripts in response to nutrient stress (PubMed:31101919). Also acts on free nicotinamide adenine dinucleotide molecules: hydrolyzes NAD(H) into NMN(H) and AMP, and NADPH into NMNH and 2',5'-ADP (PubMed:12790796). May act to regulate the concentration of peroxisomal nicotinamide nucleotide cofactors required for oxidative metabolism in this organelle (PubMed:12790796). Regulates the levels of circadian clock components PER1, PER2, PER3 and CRY2 in the liver (By similarity). a 5'-end NAD(+)-phospho-ribonucleoside in mRNA + H2O = a 5'-end phospho-adenosine-phospho-ribonucleoside in mRNA + beta-nicotinamide D-ribonucleotide + 2 H(+) H2O + NAD(+) = AMP + beta-nicotinamide D-ribonucleotide + 2 H(+) H2O + NADH = AMP + 2 H(+) + reduced beta-nicotinamide D-ribonucleotide H2O + NADPH = adenosine 3',5'-bisphosphate + 2 H(+) + reduced beta-nicotinamide D-ribonucleotide Binds 3 Mg(2+) ions per subunit. Binds 1 zinc ion per subunit. Optimum pH is 8-9. Homodimer (PubMed:31875550). Homodimerization is essential for its catalytic activity and protein stability (PubMed:31875550). Interacts (via ANK repeats) with BLMH (PubMed:31875550). Localizes to cytoplasmic granules in the presence of BLMH. Belongs to the Nudix hydrolase family. NudC subfamily.