Fig. 1. Sequencing of p43 by nanoelectrospray tandem mass spectrometry. m/z, mass-to-charge ratio. (A) Mass spectrum of the unfractionated digest of the p43 doublet band. Trypsin autolysis products are marked with asterisks. Tryptic peptides whose entire sequences were determined are designated with T. Tryptic peptides sequenced partially and retrospectively matched to the full-length sequence are designated with t. (B) Mass spectrum of product ions resulting from fragmentation of peptide precursor ion T₄²⁺ from (A). Interpretation of these mass spectra relative to those obtained from esterified peptides allowed assignment of y-ions and sequence determination.