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. Author manuscript; available in PMC: 2009 Dec 18.
Published in final edited form as: Anal Chem. 2007 Jan 24;79(5):2158–2162. doi: 10.1021/ac0620819

Figure 1.

Figure 1

MALDI mass spectra of the peptide LVNELTEFAK derived from bovine serum albumin after tryptic digestion, differential labeling with 16O/18O at a ratio of 1:1 and isoelectric focusing. The sample in Panel A was digested with soluble trypsin at a protease: substrate ratio of 1:50, followed by addition of PMSF and centrifugal ultrafiltration post-labeling. The sample in Panel B was subjected to the same procedures as a, save initial proteolytic digestion with immobilized trypsin,