ROLE OF GUANOSINE TRIPHOSPHATE IN FERRIC ION-LINKED FENTON CHEMISTRY

We measured the production of reactive hydroxyl radical (OH.) by Fe2itself or complexed with nucleotide triphosphates or tripolyphosphate (TPP). Coumarin-3-carboxylic acid (3-CCA) reacts with the OH. produced by Fe2+, Fe3+ or Cu2+ plus ascorbate and with various iron complexes. We measured in real time the increased fluorescence of 3-CCA after hy droxylation to 7-hydroxy-coumarin-3-carboxylic acid (7-OHCCA). Phospha te-buffered solutions do not affect the yield of Fe2+-linked OH. as do other organic buffer solutions. Our results show that guanosine triph osphate enhances the Fe2+-linked production of OH.. We also tested ino sine triphosphate, adenosine triphosphate and xanthine triphosphate fo r their capacity to produce OH. with Fe2+. Inosine triphosphate is the most effective nucleotide in the production of OH.. However, the Fe2-mediated yield of OH. is greater in the presence of TPP compared to t he nucleotide triphosphates. Organic buffers as well as the purine and ribose portion of nucleotides compete for OH. and decrease the yield of fluorescent 7-OHCCA. We also decreased the yield of OH. by adding g uanosine to the Fe2+/TPP-generating system. Adenosine, ribose and deox yribose also react with Fete-generated OH.. The decreased yield of 7-O HCCA occurs because the ribose and purine part of the molecule reacts with OH.. The maximal production of reactive OH., compared to all nucl eotides and phosphates tested, occurs with a ratio of 2 TPP/Fe2+ compl ex. In conclusion, the real-time measurement of the production of fluo rescent 7-OHCCA provides a convenient means for measuring chemically g enerated OH.. The TPP/Fe2+-generating mixture, in the presence of 3-CC A, can be used to study the scavenging ability of other competing mole cules. (C) 1996 by Radiation Research Society