Pro(anti)oxidant Properties of Amino Acids and Their Derivatives in The Presence of Fe<sup>2+</sup> and Cu<sup>2+</sup> Ions
Fluorescent probe, terephthalic acid, was used for rapid analysis of the ability of amino acids and their derivatives to accept and/or promote the formation of HO˙ radicals in the Cu<sup>2+</sup>-H<sub>2</sub>O<sub>2</sub>, Fe<sup>2+</sup>/EDTA-H<sub>2</sub>O<sub>2</sub> systems. In the concentration range of 0.005-30 mM., according to the increase in IC<sub>50</sub>, amino acids are ranked as follows: Trp < Phe ≤ Met ≤ His < Gly ≤ Glu < α-Ala < Cys << β-Αla << Tau (system with Cu<sup>2+</sup>); His ≤ Met < Trp ≤ Cys << β-Αla < Tau ≤ Glu < α-Ala < Gly (system with free Fe<sup>2+</sup>). In the presence of copper(II), Cys and its derivatives, Glu, α-Ala, His (S) intensify HO˙ formation, and act as antioxidants in molar ratio of S:Cu<sup>2+</sup> > 2:1, only for His this ratio is ≥1:1. Cys is also a prooxidant in the system with Fe<sup>2+</sup>/EDTA.