Fig. 3.

Mass spectrum of LysC peptide 630–644 from LysC digests of unphosphorylated (dashed line) and phosphorylated (solid line) recombinant AMII. The measured masses of the peptides were 1,444.76 and 1,524.73, respectively, a difference of 79.97 caused by phosphorylation. The parent peaks have m/z values of 482.59 and 509.25 because the ions were triply charged. The peak at 476.58 in the phosphorylated peptide sample resulted from neutral loss of phosphate, establishing that the peptide is phosphorylated. The fragmentor voltage was increased from the usual 235 V to 275 V to enhance the neutral loss of H₃PO₄.