High-resolution imaging and proteomics of peptide fragments by TOF-SIMS

Thyroglobulin is an iodinated glycoprotein (m.w. 660 kD) required for the storage and formation of thyroid hormone. Thyroglobulin was digested by trypsin in distilled water and the resulting peptides were identified by TOF-secondary ion mass spectrometry, using TFA as a matrix to catalyze the ionization of the peptides. Cryostate sections of pig thyroid glands were incubated with trypsin in distilled water, followed by deposition of TFA. The sections were analyzed with TOF-secondary ion mass spectrometry, and the peptides formed were identified through comparison with the peptides of the thyroglobulin reference sample. The thyroglobulin fragments were localized in the thyroid follicle cells with a spatial resolution of 3 microns, a mass resolution m/Δm of >6000 and a mass accuracy o