Tyrosine deprotonation in peptides yields preferential electron detachment upon NETD or UVPD, resulting in prominent N-C alpha bond cleavage N-terminal to the tyrosine residue. UVPD of iodo-tyrosine-modified peptides was used to generate localized radicals on neutral tyrosine side chains by homolytic cleavage of the C I bond. Subsequent collisional activation of the radical species yielded the same preferential cleavage of the adjacent N-terminal N-C alpha bond. LC-MS/MS analysis of a tryptic digest of BSA demonstrated that these cleavages are regularly observed for peptides when using high-pH mobile phases.