Side Chain Cleavage in TEMPO-assisted Free Radical Initiated Peptide Sequencing (FRIPS): Amino Acid Composition Information

摘要

In tandem mass spectrometry, side-chain losses are known to provide information on the presence of certain amino acid residues, which can improve peptide identification. In this study, we examine whether side-chain losses also occur in free-radical-initiated peptide sequencing mass spectrometry (FRIPS MS). All four peptides examined here, i.e., ALPMHIR, YRPPGFSPFR, RPPGFSPYR, and YGGFLRRIRPKLK, showed extensive small group losses in the so-called (M center dot-X) region. Furthermore, peaks due to small group loss accompanying backbone fragmentations were also extensively observed. The observed small group losses, either radical or neutral side-chain losses, confirmed the presence of certain amino acids, even exhibiting signature peaks for isoleucine and leucine. In addition, mechanisms for small group losses in FRIPS MS are proposed.