Photochemistry of reduced pterins

M. LAURA DÁNTOLA, ANDRÉS H.THOMAS, CAROLINA LORENTE, ALBERO L. CAPPARELLI, ANDRÉ M. BRAUN Y ESTHER OLIVEROS.

Riezlern, Austria

Workshop; Photochemie Optische Spektroskopie Sesorik; 2006

Reduced pterin derivatives, such as 7,8-dihydropterins and 5,6,7 ,8-tetrahydropterins, have anti-oxidant properties and are also known as potent scavengers of reactive oxygen species (ROS )(a), in both in vitro and in vivo conditions. However, under certain conditions, 7,8-dihydropterin derivatives have been observed to act as enhancers of ROS production(b). The aim of the present work was to define the conditions under which reduced pterins can act as ROS scavengers or ROS producers, respectively. The techniques used to investigate the behavior of reduced pterins were UV/VIS spectrophotometry, high-performance liquid chromatography (HPLC) and temperature-stability measurements in aerated aqueous solutions. Singlet oxygen (1O2) production and 1O2-quenching by reduced pterins, as well as production of 1O2 during their photolysis were studied for 6-hydroxymethyl- 7,8-dihydropterin, 7,8-dihydrobiopterin, 7,8-dihydroneopterin and 6-formyl- 7,8-dihydropterin. Result show that reduced pterins have a negligible quantum yield of 1O2 production , a  high rate constant of 1O2 quenching ( kt ) indicating that these molecules are good scavengers of 1O2 (anti-oxidant role). 7,8-Dihydropterins are not involved in ROS production. However, when these compounds were irradiated at wavelengths where photolysis products (mainly the corresponding pterin) may also be excited, 1O2 was produced in significant amounts and its production was found to be dependent on the nature of the substituent at position 6. (a) Weiss,G; Fuchs, D.; Hausen, A.; Reibnegger, G.; Wemer, E.R.; Wemer- Felmayer, G.; Semenitz, E.; Dierich, M.P. and Wachter, H. (1993) FEBS letter, 321,;89-92. (b) Milstien Sheldon, Katusic, Zvonimir (1999) Biochemical and Biophysical Research Comunications, 263 (3) 681-684.