Kinetics of the interaction of sulfate and hydrogen phosphate radicals with small peptides of glycine, alanine, tyrosine and tryptophan.
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.
Bosio
Gabriela
G
Instituto de Investigaciones Físicoquímicas Teóricas y Aplicadas (INIFTA) Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, Argentina.
Criado
Susana
S
Massad
Walter
W
Rodríguez Nieto
Felipe J
FJ
Gonzalez
Mónica C
MC
García
Norman A
NA
Mártire
Daniel O
DO
D000409:Alanine / Q000737:chemistry*; D005998:Glycine / Q000737:chemistry*; D007700:Kinetics; D010455:Peptides / Q000737:chemistry*; D010710:Phosphates / Q000737:chemistry*; D010777:Photochemistry; D013431:Sulfates / Q000737:chemistry*; D014364:Tryptophan / Q000737:chemistry*; D014443:Tyrosine / Q000737:chemistry*
D010455:Peptides; D010710:Phosphates; D013431:Sulfates; D014443:Tyrosine; D014364:Tryptophan; D000409:Alanine; D005998:Glycine