Nicotinamide guanine dinucleotide sodium salt (NGD) is a synthetic analog of nicotinamide adenine dinucleotide (NAD), featuring guanine in place of adenine. It serves as a specialized substrate in biochemical research, particularly for phosphodiesterases and ADP-ribosyl cyclases. Due to its structural similarity to NAD but lack of activity with most NAD-dependent dehydrogenases, NGD enables the study of enzyme mechanisms, cyclic nucleotide signaling, and ADP-ribosylation processes without interference from endogenous NAD pathways. It is commonly used in assays to investigate phosphodiesterase activity and the formation of cyclic GDP-ribose, contributing to research in cellular signaling and enzyme specificity.