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 RNAs; in contrast to the canonical N7 methylguanosine (m7G) cap, the NAD cap promotes mRNA decay (By similarity). Mediates the hydrolysis of some nucleoside diphosphate derivatives (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 Binds 3 Mg(2+) ions per subunit. Binds 1 zinc ion per subunit. Homodimer. Belongs to the Nudix hydrolase family. NudC subfamily.