title: Peptide structure modifications: effect of radical species generated by controlled gamma ray irradiation approach.
abstract: The present work aimed at evaluating the radiolysis effect upon a set of peptides, most of them involved in physiological functions. To generate reactive radical species, a Co(60) source (up to 15 kGy) was used for controlled gamma irradiation of some peptide solutions including derivatives attaching the stable free radical Toac (2,2,6,6-tetramethypiperidine-1-oxyl-4-amino-4-carboxylic acid). Regardless of the peptide sequence, a nonlinear and progressive degradation of a total of nine peptides was detected. The results were interpreted in the light of the half-life dose (D(1/2)) parameter which represents the dose necessary for 50% peptide structure degradation. The vasoactive angiotensin II (AngII)'s analogue Ang-(1-7) showed greater stability towards gamma ray radiation than bradykinin (BK), Toac(0)-BK, Pro(4)-BK (D(1/2) around 4 and 2 kGy, respectively) which decreased to about 0.5-1.0 kGy in the case of acetyl-α-melanocyte-stimulating hormone (Ac-α-MSH) and substance P (SP). In terms of peptide structural modifications, the data acquired from different analytical methods suggested a Phe to Tyr (or its ortho and/or meta isomers) transformation as a consequence of the hydroxyl moiety insertion. Noteworthy, this effect seemed to be position-dependent as only Phe located at or near the C-terminal portion seemed to display this transformation. In contrast, Met is comparatively more easily oxidized, thus allowing to conclude that gamma irradiation may induce a complex position and/or sequence-dependent effect on peptides. As previously applied for BK, some irradiated peptides were submitted to their by-products purification, indeed a complementary target of the present approach for development of uncommon analogues for further structure-function investigation.
authors.affiliation: Department of Biophysics, Paulista Medical School, Federal University of Sao Paulo, Rua Três de Maio, 100, Sao Paulo 04044020, Brazil.
authors.forename: Renata de Freitas Fischer
authors.initials: Rde F
authors.lastname: Vieira
authors.forename: Daniela Teves
authors.initials: DT
authors.lastname: Nardi
authors.forename: Nanci
authors.initials: N
authors.lastname: Nascimento
authors.forename: José César
authors.initials: JC
authors.lastname: Rosa
authors.forename: Clovis Ryuichi
authors.initials: CR
authors.lastname: Nakaie
mesh_terms: D000818:Animals; D003497:Cyclic N-Oxides / Q000737:chemistry; D005720:Gamma Rays; D005748:Gastric Fundus / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D015394:Molecular Structure; D009119:Muscle Contraction / Q000187:drug effects; D010455:Peptides / Q000737:chemistry / Q000494:pharmacology / Q000528:radiation effects*
chemical_list: D003497:Cyclic N-Oxides; D010455:Peptides; C037109:2,2,6,6-tetramethylpiperidine-N-oxide-4-amino-4-carboxylic acid