Has ADP-ribosyltransferase activity toward GLP1R. L-arginyl-[protein] + NAD(+) = H(+) + N(omega)-(ADP-D-ribosyl)-L-arginyl-[protein] + nicotinamide Abundantly expressed in cardiac and skeletal muscle. Low levels also found in lung. Belongs to the Arg-specific ADP-ribosyltransferase family.