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. The NAD-cap is present at the 5'-end of some mRNAs and stabilizes RNA against 5'-processing. Has preference for mRNAs with a 5'-end purine. Catalyzes the hydrolysis of a broad range of dinucleotide pyrophosphates. 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 Divalent metal cations. Mg(2+) or Mn(2+). Binds 1 zinc ion per subunit. Homodimer. Belongs to the Nudix hydrolase family. NudC subfamily.