CONICET | Buscador de Institutos y Recursos Humanos

Folic acid, or pteroyl-L-glutamic acid (PteGlu) isa conjugated pterin derivative that is used in dietary supplementation as asource of folates, a group of compounds essential for a variety ofphysiological functions in humans. Photochemistry of PteGlu is importantbecause folates are not synthesized by mammals, undergo photodegradation andtheir deficiency is related to many diseases. We have demonstrated that usual commercial PteGlu is unpurifiedwith the unconjugated oxidized pterins 6-formylpterin (Fop) and 6-carboxypterin(Cap). These compounds are in such low amounts that a normal chromatographiccontrol would not detect any pterinic contamination. However, thefluorescence of PteGlu solutions is due to the emission of Fop and Cap and thecontribution of the PteGlu emission, much lower, is negligible. This is becausethe fluorescence quantum yield (ΦF) of PteGlu is extremely weakcompared to the ΦF of Fop and Cap. Likewise, the PteGluphotodegradation upon UV-A radiation is an oxidation photosensitized byoxidized unconjugated pterins present in the solution, and not a processinitiated by the direct absorption of photons by PteGlu.In brief, the fluorescence and photochemical properties of PteGlu solutions, prepared usingcommercially available solids, are due to their unconjugated pterins impuritiesand not to PteGlu itself. This fact calls into question many reported studieson fluorescence and photooxidation of this compound.