Beta-Tubulin identification and limitations of peptide mass fingerprinting.

The identification of tubulin from peptide mass fingerprinting matches with LC-MS/MS data for the majority of peptides. However, assignment for the 1249.585 and 1696.805 peptides were inaccurate. The 1249.585 peak was not assigned in the MALDI-TOF data. The observed mass of 1696.805 and data in Table 3 are from ProFound and assigned to peptide sequence ALTVSELTQQMFDSK (data denoted with an asterisk *). Peptide fragmentation data using LC-MS/MS suggests this assignment is incorrect and that the correct sequence is NSSYFVEWIPNNVK with deamidation at the amino-terminus yielding the sequence DSSYFVEWIPNNVK (MH+ = 1697.817 expected, 1697.813 observed, −2.4 ppm error). Beta-Tubulin identification and limitations of peptide mass fingerprinting.