Are pterins able to modulate oxidative stress?
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Pterins (also known as pteridines) are common animal colorants that constitute heterocyclic compounds and have the highest nitrogen content of any pigment analyzed from animals. It has been reported that pterins modulate oxidative stress as these molecules are able to scavenge free radicals. Previous reports suggest three possible mechanisms that are responsible for scavenging free radicals; these are electron transfer (ET) reaction, hydrogen atom transfer (HAT) and radical addition. In this paper, the facility to scavenge free radicals (antiradical power) of pterins is analyzed, using density functional theory calculations and considering two possible mechanisms: ET and HAT. For the electron transfer process, considering the electron donor facility of the free radical scavenger molecules, vertical ionization energy of pterins indicates that the antiradical power of those pterins is lower than the antiradical power of any carotenoids (except for tetrahydrobiopterin). In terms of the HAT mechanism, the bond dissociation energy involved in the removal of one hydrogen atom from pterins is higher than for carotenoids (except for sepiapterin and 7,8-dihydrobiopterin). It can be expected that the most reactive molecules are those that have the smallest dissociation energy since the dissociation of the hydrogen atom is the first step of the reaction. This could indicate that some pterins are depicted as poorer antiradicals than carotenoids in terms of the HAT mechanism. Further studies focusing on the third mechanism (radical addition) and the kinetics of the reactions are necessary in order to fully understand the antiradical power of these substances. For this reason, work continues in order to clarify these aspects.
Keywordspterins Animal pigments Antioxidants Radical scavengers Free radicals Oxidative stress
This study was made possible due to funding from the Consejo Nacional de Ciencia y Tecnología (CONACyT), as well as resources provided by the Instituto de Investigaciones en Materiales IIM, UNAM. The work was carried out, using KanBalam supercomputer, provided by DGSCA, UNAM. We would like to thank The Dirección General de Servicios de Computo Académico (DGSCA) of the Universidad Nacional Autónoma de México for their excellent and free supercomputing services. We would also like to thank Caroline Karslake (Masters, Social Anthropology, Cambridge University, England) for reviewing the grammar and style of the text in English. The authors would like to acknowledge both Sara Jiménez Cortés and María Teresa Vázquez for their technical support. A.M. is grateful for financial support from the Ministerio de Educación y Ciencia de España (SAB2006-0192) and DGAPA-UNAM-México. A.B. was supported by the projects CGL2007-60369 and POL2006-05175 funded by the Spanish Ministry of Education and the European Regional Development Fund.
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