HALOGENATED SPECIES - Oxidation of Amino Acids, Peptides, and Proteins: Kinetics and Mechanism - page 97

(a)
(b)
Figure 3.11. Comparison of tryptophan oxidation by measurement of intrinsic fluores-
cence. (a) The reaction mixtures consisted of 1.0 mM tryptophan (control) and 1.0 mM
Tau-NHBr, Tau-NHCl, HOCl, or HOBr in phosphate buffer saline (PBS), pH 7.4 at
25°C. The intrinsic fluorescence was measured 2 minutes after the addition of oxidants
(λ ex 295 nm, λ em 360 nm). (b) Dose-dependent effect of halamines on tryptophan con-
sumption. The reaction mixtures consisted of 1.0 mM tryptophan and the indicated
concentrations of halamines in PBS, pH 7.4 at 25°C. The results shown are representa-
tive of three experiments (adapted from ximenes et al. [123] with the permission of
Elsevier Inc.).
transfer with rate constants k 2 and k 3 , respectively, to generate ClO 2 . All three
rate constants decrease in rate constants with an increase in pH (Fig. 3.13b).
The values of k 1 , k 2 , and k 3 at pH 7.0 were determined as 7.5 × 10 3 /M/s,
1.9 × 10 4 /M/s, and 1.5 × 10 3 /M/s, respectively. The production of ClO 2 as well
as of HOCl may cause heme bleaching and the modification of amino acids.