PNNL

Abstract

Angiotensin II (DRVYIHPF) and two analogs (DRVYIAPA, and DRVAIHPA) 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. Additional ions in the CID and SID spectra suggested formation of Tyr + 3O and a small amount of Phe + O. Two analogs were also studied, one in which His and Phe were replaced by Ala (DRVYIAPA) and the other in which Tyr and Phe were replaced by Ala (DRVAIHPA). Exposure of DRVYIAPA to ozone resulted in the addition of one and three oxygen atoms, while DRVAIHPA showed only the addition of three oxygen atoms. Tandem mass spectra of these adducts confirmed the formation of Tyr + 3O in addition to Tyr + O and His + 3O. Other noteworthy minor oxidation products were observed from these analogs including Tyr + 34 u, His + 34 u, and His + 82 u. Modified reaction schemes for peptide ozonolysis are proposed which account for each of these newly observed adducts.