Study of interaction of styrene oxide with angiotensin by mass spectrometry

The present study describes how mass spectrometry was extensively applied to the characterization and quantification of modified amino acids within the polypeptide chain of Angiotensin I, chosen as model substrate, combining the use of fast atom bombardment mass spectrometry with gas chromatography--mass spectrometry. The reaction products after in vitro incubation of Angiotensin I with styrene oxide, a well known carcinogen, under different conditions, have been characterized: a prominent reactivity of several potential nucleophilic sites of Angiotensin I was shown, including two histidine residues and a tyrosine residue; it is worth noting that it has never been stated that tyrosine is highly reactive with styrene oxide. The results obtained demonstrate the usefulness of mass spectrometry for the structural determination of chemically modified amino acids in peptides and proteins, and the presence of a reliable relationship between reaction conditions and the production of alkylated amino acids. This characterization procedure offers the possibility of identifying reactive sites following exposure to unknown alkylating agents.