2′-Deoxyguanosine 5′-monophosphate (5′-Deoxyguanylic acid; dGMP) disodium hydrate is an oxidizable target of the photosensitizer pterin (PT) and can be used to evaluate the photosensitizing properties of biopterins (such as Bip, Fop and Cap) . Pterin causes a photosensitive reaction of dGMP under UV-A radiation, causing damage to DNA molecules. There are two main mechanisms for the photosensitive oxidation of purine nucleotides by pterin in vitro: one is the hydrogen abstraction reaction of electron transfer from dGMP to the triplet excited state of pterin (type I mechanism), and the other is the interaction between dGMP and pterin. The reaction produces singlet molecular oxygen (1O2) (Type II mechanism)^[1][2].