| Abstract: | Proline and hydroxyproline when exposed to the hydroxyl free radical generating system of ADP-Fe(II)-H2O2 yielded long-lived free radicals. An analysis of the electron paramagnetic resonance spectra of the long-lived hydroxyl free radical adducts of proline and hydroxyproline is consistent with a free electron on a nitroxyl group interacting with the nitrogen atom as well as with three separate protons. In the case of proline, nitroxide formation was observed under the influence of tert-butyl-hydroperoxide, giving a similar EPR spectrum (Lin, J.S., Tom, T.C. and Olcott, H.S. (1974) J. Agr. Food Chem. 22, 526-528); however, the hydroxyl free radical adduct of hydroxyproline has not been described yet. In the case of the proline nitroxide radical, two of the three protons involved interact with the free electron equivalently. The coupling constants for the hydroxyl free radical adduct of proline are AN = 1.58 mT, AH1 beta = AH2 beta = 2.13 mT, AH3 beta = 1.77 mT and for hydroxyproline are AN = 1.54 mT, AH1 beta = 2.56 mT, AH2 beta = 2.03 and AH3 beta = 1.51. The data are consistent with the amine nitrogen of proline and hydroxyproline being oxidized to a nitroxyl group and the free electron of the nitroxyl interacting with the beta-protons of these amino acid hydroxyl free radical adducts. |
