Kinetics of the interaction of sulfate and hydrogen phosphate radicals with small peptides of glycine, alanine, tyrosine and tryptophan

Abstract

The kinetics and mechanism of the oxidation of Glycine (Gly), Alanine (Ala), Tyrosine (Tyr), Tryptophan (Trp) and some di-(Gly-Gly, Ala-Ala, Gly-Ala, Gly-Trp, Trp-Gly, Gly-Tyr, Tyr-Gly), tri-(Gly-Gly-Gly, Ala-Gly-Gly) and tetrapeptides (Gly-Gly-Gly-Gly) mediated by sulfate (SO(4) (-)) and hydrogen phosphate (HPO(4) (-)) radicals was studied, employing the flash-photolysis technique. The substrates were found to react with sulfate radicals (SO(4) (-), produced by photolysis of the S(2)O(8)(2-)) faster than with hydrogen phosphate radicals (HPO(4) (-), generated by photolysis of P(2)O(8)(4-) at pH = 7.1). The reactions of the zwitterions of the aliphatic amino acids and peptides with SO(4) (-) radicals take place by electron transfer from the carboxylate moiety to the inorganic radical, whereas those of the HPO(4) (-) proceed by H-abstraction from the alpha carbon atom. The phenoxyl radical of Tyr-Gly and Gly-Tyr are formed as intermediate species of the oxidation of these peptides by the inorganic radicals. The radical cations of Gly-Trp and Trp-Gly (at pH = 4.2) and their corresponding deprotonated forms (at pH = 7) were detected as intermediates species of the oxidation of these peptides with SO(4) (-) and HPO(4) (-). Reaction mechanisms which account for the observed intermediates are proposed.

A kinetic study of the reactions of sulfate and dihydrogen phosphate radicals with epicatechin, epicatechingallate, and epigalocatechingallate

“…Since the reactions of inorganic radicals with organic molecules important for biological processes are a relevant domain of research, the reaction of sulfate and phosphate radical anions with such molecules has been investigated in the literature [12][13][14]. In an attempt to make a contribution to the free radical chemistry of EC, ECG, and EGCG, in this study we investigated the reactions of sulfate and dihydrogen phosphate radicals with these flavonoids.…”

Biophysical properties and cellular toxicity of covalent crosslinked oligomers of α-synuclein formed by photoinduced side-chain tyrosyl radicals

“…Both the Ru III (bpy) 3 3 þ and SO 4 À species are potent one-electron oxidants capable of oxidizing primarily aromatic and sulfurcontaining residues [32][33][34]. The reduction potentials of sidechain and backbone-derived radicals indicate that the ultimate sinks for oxidizing equivalents are Tyr, Trp, and Cys residues [35].…”

Reactive Inorganic Oxy‐Species of C, N, S, and P

“…The kinetics for the oxidation of amino acids and peptides by SO 4 •− radicals have been performed (Table 5.9) [352,[377][378][379][380]. Peptides were found to be more reactive than their parent free amino acids (Table 5.9).…”

“…Aromatic amino acids had a higher reactivity than aliphatic amino acids. For example, Tyr and Trp amino acids containing peptides reacted at diffusion-controlled rate constants, which are much faster than those containing only gly and/or Ala [377]. For example, Tyr and Trp amino acids containing peptides reacted at diffusion-controlled rate constants, which are much faster than those containing only gly and/or Ala [377].…”

“…The interaction of SO 4 •− with the aromatic amino acid of the dipeptides, Trp-gly, gly-Trp, gly-Tyr, and Tyr-gly is expected to occur [377]. Figure 5.…”