PubMed · 13172197
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R E MATTHEWS, J D SMITH. 1954-03-20. Interconversions between 8-azapurines.. https://pubmed.ncbi.nlm.nih.gov/13172197/
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Formation of 8-nitroguanosine may be characterized as nucleic acid modification induced by nitric oxide (NO). We show here that 8-nitroguanosine is a highly redox-active nucleic acid derivative that strongly stimulated superoxide generation from various NADPH-dependent reductases, including cytochrome P450 reductase and all isoforms of NO synthase. This reaction involves these reductases in a redox cycling reaction via single-electron reduction of 8-nitroguanosine to form 8-nitroguanosine anion radical. One electron is then transferred from this radical to molecular oxygen. 8-Nitroguanosine formed in vivo may function as a potent redox cofactor that intensifies oxyradical generation by various NADPH/reductase-like enzymes and thus participates in diverse physiological and pathological events.
We report solid-state 23Na NMR and X-ray crystallographic results for a self-assembled G-quadruplex channel formed by a guanine nucleoside, 5'-tert-butyl-dimethylsilyl-2',3'-O-isopropylidene guanosine (G 1). The study provides an unambiguous 23Na NMR identification for the Na+ ions inside a lipophilic G-quadruplex channel. The crystalline nature of the sample yields a remarkably high resolution in the 23Na multiple-quantum magic-angle spinning (MQMAS) spectrum, making it possible to extract very accurate 23Na NMR parameters for each of the three crystallographically distinct Na sites. The observation of a single Na+ ion from a 9-kDa system demonstrates the potential of solid-state 23Na NMR as a complementary technique to X-ray for detecting Na+ ions in biological structures.
Density functional calculations at the B3LYP/6-311+G(2d,p)//pBP/DN level predict all cationic adducts combining guanine, at either its N2, O6, N7, or C8 positions, with phenylnitrenium ion, at either its N, 2, or 4 positions, to be lower in energy than the separated reactants. This relative stability of all adducts is preserved after addition of aqueous solvation free energies computed at the SM2 level, although some leveling of the adduct relative energies one to another is predicted. Cations having the lowest relative energies in solution correspond structurally to those adducts most commonly found when guanine reacts with larger, biologically relevant nitrenium ions in vitro and in vivo. One of these, the N-C8 adduct, is stabilized both by a rearomatized phenyl ring and by the operation of an anomeric effect not found in any of the others. On the basis of energetic analysis, direct conversion of an N-N7 cation to an N-C8 cation according to a previously proposed mechanism is unlikely; however, an alternative rearrangement converting a 2-N7 cation to an N-C8 cation via the intermediacy of a five-membered ring may be operative in nitrenium ions with aromatic frameworks better able than phenyl to stabilize endocyclic cationic charge.