The CT peptides were identified as a1 and b6 tubulins by accurate mass and are labeled in Figure . The notation used includes "CT" for C-terminal CNBr peptide and the corresponding tubulin type (a-or b-) and isotype, as well as PTMs. Thus, "a1CT" refers to the C-terminal-most peptide produced by CNBr cleavage of a1 tubulin, and "a1CT-Y" refers to the C-terminal most CNBr peptide lacking the terminal tyrosine. It is important to note that, owing to the location of the Figure . MALDI reveals C-terminal peptides generated following CNBr cleavage from predominantly one isotype of alpha tubulin (a-1) and one isotype of beta tubulin (β-6). Figure shows the full m/z region containing peptides from a-and β-tubulins. Denoted in the figure are signals from both alpha and beta isotypes as well as the internal standard used for mass calibration. Figure shows an expanded region containing the c-terminal peptides of a1 tubulin, including the full length peptide (noted α1CT; m/z 2861), the de-tyrosinated CT peptide (a1CT-Y; m/z 2697), and the peptide of intermediate mass, labeled (a1CT-Y+'X'; m/z 2805). cleavage site, the peptides from CNBr ("CT's") include more amino acids than the ~15 residues in the CTT tail peptides. These sequence differences are outlined in Scheme 1.