OT interrupted protein synthesis rate of annexin A1. MS spectra of 1702.5 m/z fragment from spot #20 of lysates of cells grown in the presence of natural amino acids (A), 50% 15 N enriched medium and 0 μM OT for 12 h (B) and 50% 15 N enriched medium and 50 μM OT for 12 h (C), 50% 15 N enriched medium and 0 μM OT for 48 h (D), 15 N enriched medium and 50 μM OT for 48 h (E). The synthesis rate of a protein was based on the isotopomer distribution of these spectra. (F). shows the MS/MS spectrum of this fragment in the “lift” mode. Sequences were confirmed from the labeled b- and y-ions in the spectrum using a Mascot database search.