Specifically acts as an arginine mono-ADP-ribosylhydrolase by mediating the removal of mono-ADP-ribose attached to arginine residues on proteins. H2O + N(omega)-(ADP-D-ribosyl)-L-arginyl-[protein] = ADP-D-ribose + L-arginyl-[protein] alpha-NAD(+) + H2O = ADP-D-ribose + H(+) + nicotinamide Binds 2 magnesium ions per subunit. Synergistically stimulated by magnesium and dithiothreitol (DTT) in vitro. Monomer. Belongs to the ADP-ribosylglycohydrolase family.