Reactivity of glycyl-amino acids toward hydroxyl radical in neutral aqueous solutions.

増 田高広,岩 下尚美,篠 原広行,近 藤 正春:東 京都立大学理学部化学科 東京 都世田谷区深沢2-1-1 T158 Reactivity of dipeptide/Hydroxyl radicals/Rate constant Rate constants for reactions of hydroxyl radicals with several glycyl-amino acids were determined by a competition method using p-nitrosodimethylailine as a reference compound. For glycyl-aliphatic amino acids, the enhancement of reactivity was observed as compared with the corresponding free amino acids. The reactivity was explained qualitatively in terms of partial reactivities assigned to each C-H bond of the dipeptides. For glycyl-aromatic amino acids, the rate constants were found to be almost equal to those of the corresponding free amino acids. The reactivity of a protein toward hydroxyl radical was well understood by summation of the rate constants, corrected by steric factors, of amino acid residues located on surface of the protein. The enhanced reactivity of the aliphatic peptides was interpreted in terms of the difference in interaction energy between NH2and NH3+-forms of an aliphatic amino acid, which was calculated for the system including glycine and hydroxyl radical ac cording to CNDO/2 method.