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. Author manuscript; available in PMC: 2022 Apr 3.
Published in final edited form as: J Proteome Res. 2022 Feb 27;21(4):891–898. doi: 10.1021/acs.jproteome.1c00894

Figure 5. Abundance profiles of tryptic peptides mapping to a) GAPDH and b) SCG2 proteins in cerebrospinal fluid.

Figure 5.

Three groups of human cerebrospinal fluid samples were analyzed by DIA-MS: Alzheimer’s disease, Parkinson’s disease, and healthy age and sex-matched controls. Unique peptides mapping to the proteins a) GAPDH and c) SCG2 report quantitatively on their relative expression ratios. The protein-level display integrates the mean values from all peptide-level results (box-and-whisker plot at left), with the expression ratio for each individual peptide and the group shown in the bar graphs at right. b) GAPDH has been observed as three proteoforms which form homo-tetramers from human cell lines including HEK-tsa. Intact mass spectra of the monomeric form reveal a canonical form, a persulfide-modified form, and a glutathione-modified form. Reported masses represent average masses and ppm mass error from the calculated theoretical average mass. d) SCG2 is proteolytically processed to produce several peptides, has a sulfotyrosine, and can be phosphorylated at several serine residues.