ONE-ELECTRON REACTIONS IN BIOCHEMICAL SYSTEMS AS STUDIED BY PULSE RADIOLYSIS .2. RIBOFLAVIN

When riboflavin is subjected to high-energy irradiation in the presence of formate it becomes reduced to the semiquinone by hydrated electrons, CO2-, or COOH. Rate constants for the reactions are tabulated. The semiquinone has pK's of 2.3 and 8.3. Improved spectra have been determined for the forms of the semiquinone present at pH -1.1, 5.1, and 11.4. The form present at pH -1.1 is stable, but the forms present at pH 5.1 and 11.4 disappear in second-order reactions with rate constants of 2k = 1.14 × 109 and 7 × 108 M-1, respectively. The form present at pH 5.1 is uncharged. Electron transfer from the adenine ring to riboflavin is demonstrated. Riboflavin itself has been found to undergo a change in protonation at H0~-8. © 1969, American Chemical Society. All rights reserved.