Radiolysis of 4-thiouracil and of the 4-thiouracil moieties of 4-thiouridine and transfer ribonucleic acid from Escherichia coli in aqueous solutions

Abstract

4-Thiouracil, 4-thiouridine and tRNA from Escherichia coli were irradiated with X-rays in air-saturated solutions and the radiolysis of the 4-thiouracil moieties was determined spectrophotometrically. The dose-effect curves were exponential, giving initial yields of destruction ( G value) of 3.22 for thiouracil, 2.45 for thiouridine and 0.31 for the thiouracil residues in tRNA. The thiopyrimidine residues were more radiolabile than the corresponding oxygen analogues, as the G values found for uracil and uridine under the same conditions were 2.28 and 1.83, respectively. The following radiolysis products were demonstrated in irradiated thiouracil solutions: uracil, thiouracil disulfide, isobarbituric acid, di-isobarbituric acid and inorganic sulfate. Radiolysis products identified in irradiated thiouridine solutions were uridine, thiouridine disulfide and sulfate.