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 (PubMed:11361135). 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. kcat is 1.5 sec(-1) for NADH. kcat is 0.6 sec(-1) for NAD(+). kcat is 0.6 sec(-1) for ADP-ribose. Homodimer. Present with 846 molecules/cell in log phase SD medium. Belongs to the Nudix hydrolase family. NudC subfamily.