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Chi-Kit Andy Siu

Chi-Kit Andy Siu

City University of Hong Kong, China

Title: Discovery and mechanistic studies of an unusual remote radical-induced side-chain loss from tyrosine-containing peptide radical cations in the gas phase

Biography

Biography: Chi-Kit Andy Siu

Abstract

Tyrosine is a constituent amino-acid residue of proteins. Because of the relatively low ionization energy of the aromatic phenol ring in its side chain, tyrosine is prone to be oxidized. The resulting one-electron oxidized tyrosyl radical is an important intermediate in many redox reactions of protein radicals. The intrinsic chemical properties of tyrosyl radical can be revealed from the fragmentations of tyrosine-containing peptide radical cations in the gas phase. The peptide fragments also provides invaluable sequence information that can be applied in mass spectrometry-based protein analyses. Upon ionization in the gas phase, a variety of tyrosyl radical tautomers can be generated and subsequently undergo radical-induced bond cleavages normally in the vicinity of the tyrosine residue. We have recently discovered an unusual radical-induced bond cleavage at the side chain of an amino-acid residue remote from the tyrosine. The plausible reaction mechanisms at the atomic and electronic levels have been examined experimentally using collision-induced dissociation for peptide models and their isotope-labeled and chemical derivatives and theoretically using density functional theory simulations.