A PULSE-RADIOLYSIS STUDY OF THE REACTIONS OF 3-HYDROXYKYNURENINE AND KYNURENINE WITH OXIDIZING AND REDUCING RADICALS

Pulse radiolysis has been used to study the reactions of 3-hydroxykynu renine and kynurenine with solvated electrons, superoxide radicals, hy droxyl radicals and azide radicals. Both 3-hydroxykynurenine and kynur enine react with solvated electrons with diffusion controlled rate con stants (k = 2.5 . 10(10) M-1 s-1 and 2.3 . 10(10) M-1 s-1, respectivel y). Neither compound was observed to react with superoxide radicals un der our experimental conditions, an upper limit of 1.2 . 10(5) M-1 s-1 for the rate constant of this reaction was estimated for both compoun ds. However, we do observe that a stable product of autooxidation of 3 -hydroxykynurenine reacts with superoxide radicals and we calculate a lower limit for the rate of this reaction of 5.8 . 10(6) M-1 s-1. Reac tions of 3-hydroxykynurenine and kynurenine with hydroxyl radicals pro ceed with diffusion controlled rate constants (1.2 . 10(10) M-1 s-1 an d 1.3 - 10(10) M-1 s-1, respectively). The measured values for the rat e constants for reaction of 3-hydroxykynurenine kynurenine and kynuren ine with azide radicals are 2.1 - 10(10) M-1 s-1 and 4.8 - 10(9) M-1 s -1, respectively. The differences in these rate constants are attribut ed to differences in the measured oxidation potentials for 3-hydroxyky nurenine (+ 1.0 V vs. NHE) and kynurenine (+ 1.15 V vs. NHE).