Rapid Communication

Abstract

Degradation of DNA when gamma-irradiated in aqueous solutions containing cysteine can be efficiently enhanced not only with oxygen, but to the same extent also with Cu2+ ions under hypoxic conditions. The result can be explained by 'self-repair' in this system due to recombination of DNA. with RSS.-R intermediates, and repair inhibition by oxygen or copper involving RSS.-R scavenging. It is emphasized that oxygen enhancement in DNA-thiol systems may occur not only by peroxidation, via defect fixation (DNA-O2.) or thiol activation (RS-O2.), but also by the well-established inactivation of RSS.-R by oxygen. There is evidence also from literature data for a correlation between oxygen enhancement and RSS.-R stability, which varies with thiol concentration, pH and thiol structure.

Chemical Evidence for Thiyl Radical Addition to the C6-Position of a Pyrimidine Nucleoside and Its Possible Relevance to DNA Damage Amplification

“…Thiols are potent antioxidants and have been used as radioprotecting agents on account of their proficiency to act as hydrogen atom donors in radical reactions and to participate in electron-transfer processes. , Perhaps less well appreciated are observations that link physiological levels of thiols to mutagenicity in bacteria. , Under some conditions, thiols are believed to enhance DNA damage through their involvement in the formation of reactive oxygen species . Alternatively, one could consider the possibility that thiols and/or a species derived from them react directly with DNA.…”

Nature of Thiyl Peroxyl Radical: ESR and ab Initio MO Evidence for Intermolecular Stabilization of the Charge Transfer State, RS(+)OO.bul.-

“…The thiyl peroxyl radical, RSOO", has been the subject of considerable interest due to its likely involvement in the autoxidation of thiols1-13 and its implication in the oxygen enhancement effect of radiation in living systems. [4][5][6][7][8][9][10][11][12][13][14][15][16] It is formed reversibly3-5'12 by oxygen addition to radiation-produced thiyl radicals, reaction 1.…”

Ab Initio Study of Thiol Aqueous Phase Ionization Energies of Methyl Mercaptan and Cysteamine

“…Such transfer has been observed between RSand the DNA base cation radical, G'+,3,15 as well as between disulfide anion radical, RSSR*-, and DNA'+. 16 As part of an ongoing investigation on radioprotective thiols, 5,13,17,18 in this work, we employ ab initio theory to calculate the ionization energies of two thiols: methyl mercaptan and cysteamine in gas phase and in solution. By comparing these results to the previously calculated ionization energies of the four DNA bases,19 we elucidate the possible mechanisms ® Abstract published in Advance ACS Abstracts, September 15, 1994. 0022-3654/94/2098-10484$04.50/0 by which simple thiols protect DNA by electron-transfer processes and the influence of hydration on these processes.…”