Photodimerization of 6-hydroxymethyl-7,8-dihydropterin in aqueous solution under UV-A irradiation

ESTHER OLIVEROS; M. LAURA DÁNTOLA; ANDRÉ M. BRAUN; ANDRÉS H. THOMAS; CAROLINA LORENTE

Bad Hofgastein

Congreso; Central European Conference on Photochemistry (CECP2012); 2012

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: oxidized (or aromatic) pterins and 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. tetrahydrofolic acid is a coenzyme in many reactions, especially in the metabolism of amino acids and nucleic acids [1]. All organisms require reduced folate cofactors for the synthesis of a variety of metabolites. 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 reactivity of H2Hmp. In this work, the kinetics of H2Hmp consumption under UV-A irradiation in aqueous solutions at physiological pH were followed by UV/vis spectrophotometry and HPLC. 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 = 0.10 ± 0.02) was independent of O2 and reactant concentrations. Mechanistic and potential biological implications of the results obtained will be discussed. [1] R. Blakely, S. Benkovic, Chemistry and Biochemistry of Pterins. In: Folates and Pterins, Vol. 2. John Wiley & Sons, New York, 1984.