Peptide Ozonolysis: Product Structures and Relative Reactivities for Oxidation of Tyrosine and Histidine Residues

• Published in: Journal of the American Society for Mass Spectrometry 2006-09, Vol.17 (9), p.1289-1298
• Main Authors: Lloyd, Julie A., Spraggins, Jeffrey M., Johnston, Murray V., Laskin, Julia
• Format: Article
• Language: English
• Subjects: Adducts; Amino acids; Analogs; Angiotensin II - chemistry; Chemistry; Computer Simulation; Crystal structure; Exact sciences and technology; Histidine; Histidine - chemistry; Mass spectrometry; Models, Chemical; Models, Molecular; Organic chemistry; Oxidation; Oxidation-Reduction; Oxygen atoms; Ozone; Ozone - chemistry; Peptides; Peptides - chemistry; Reactivity and mechanisms; Residues; Spectrometry, Mass, Electrospray Ionization - methods; Tyrosine; Tyrosine - chemistry
• ISSN: 1044-0305; 1879-1123
• DOI: 10.1016/j.jasms.2006.05.009

Angiotensin II (DRV YI HP F) and two analogs, (DRV YI AP A and DRV AI HP A), were used as model systems to study the ozonolysis of peptides containing tyrosine and histidine residues. The ESI mass spectrum of angiotensin II following exposure to ozone showed the formation of adducts containing one, three, and four oxygen atoms. CID and SID spectra of these adducts were consistent with formation of Tyr + O and His + 3O as expected from previous work with amino acids. However, several fragment ions observed in the CID and SID spectra suggested formation of a rather unexpected adduct, Tyr + 3O, and a small amount of the Phe + O adduct. These findings were confirmed by examining two angiotensin analogs. Exposure of DRV YI AP A to ozone resulted in the addition of either one or three oxygen atoms on Tyr, while DRV AI HP A showed only the addition of three oxygen atoms—all on His. Other noteworthy minor oxidation products were observed from these analogs including Tyr + 34 Da, His + 5 Da, His + 34 Da, and His + 82 Da. The reaction rates of the peptides with ozone were found to be similar: second-order rate coefficients are 274 ± 3, 379 ± 6, and 439 ± 34 M −1s −1 for DRV YI AP A, DRV AI HP A, and angiotensin II, respectively. The relative rates indicate (1) an isolated His residue has a slightly greater ozone reactivity than an isolated Tyr residue, and (2) the reaction rates of isolated residues are not additive when both residues are present in the same molecule.