CONICET | Buscador de Institutos y Recursos Humanos

Pterins, heterocyclic compounds widespread in biological systems, are derived from 2-aminopteridin-4(1H)-one or pterin. The most common pterin derivatives are 6-substituted compounds and exist in different oxidation states. They may be separated into two classes according to this property: (a) oxidized or aromatic pterins and (b) reduced pterins. Within the latter group, 7,8-dihydropterins and 5,6,7,8-tetrahydropterins are most important due to their biological activity, e.g. dihydrobiopterin and tetrahydrobiopterin participate in the metabolism of aminoacids,1 tetrahydrofolic acid is a coenzyme in many reactions, especially in the metabolism of amino acids and nucleic acids. 2 All organisms require reduced folate cofactors for the synthesis of a variety of metabolites. Enzymes involved in folate biosynthesis are therefore targets for a variety of antimicrobial agents. 7,8-dihydro-6-hydroxymethylpterin-pyrophosphokinase catalyzes the attachment of pyrophosphate to 6-hydroxymethyl-7,8-dihydropterin (H2Hmp) to form 6-hydroxymethyl-7,8-dihydropteridine pyrophosphate, an important intermediate in the biosynthesis of folate. Little is known about the photochemical stability of H2Hmp in aqueous solutions at room temperature and physiological pH. In this work, we describe some aspects of the H2Hmp reactivity under UV-A irradiation. The kinetics of H2Hmp consumption were followed by UV/vis spectrophotometry and HPLC. Hydrogen peroxide (H2O2) production was quantified by enzymatic methods. Products were analyzed by electrospray ionization mass spectrometry. Excitation of H2Hmp leads to the formation of a dimer with a molecular mass equal to exactly twice that of the substrate. The quantum yield of H2Hmp consumption (F-H2Hmp = 0.14 ± 0.01) was independent of O2 and reactant concentrations. Mechanistic and potential biological implications of the results obtained will be discussed.