Pro(anti)oxidant Properties of Amino Acids and Their Derivatives in The Presence of Fe2+ and Cu2+ Ions

Abstract

A fluorescent probe (terephthalic acid) has been used for rapid assessment of the ability of amino acids and their derivatives to accept and/or promote the formation of HO˙ radicals in the Cu2+–H2O2, Fe2+/EDTA–H2O2 systems. In the concentration range of 0.005-30 mM, the amino acids are arranged in the following series according to the increase in IC50: Trp < Phe ≤ Met ≤ His < Gly ≤ Glu < α-Ala < Cys << β-Αla << Tau (system with Cu2+); His ≤ Met < Trp ≤ Cys << β-Αla < Tau ≤ Glu < α-Ala < Gly (system with free Fe2+). In the presence of copper(II), Cys and its derivatives, Glu, α-Ala, His (S) favored the HO˙ formation and acted as antioxidants at the S : Cu2+ molar ratio > 2 : 1 (≥1 : 1 for His). Cys is also a prooxidant in the Fe2+/EDTA system.