Effective detection of peptides containing cysteine sulfonic acid using matrix-assisted laser desorption/ionization and laser desorption/ionization on porous silicon mass spectrometry.
Cysteine sulfonic acid-containing peptides, being typical acidic peptides, exhibit low response in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. In this study, matrix conditions and the effect of diammonium hydrogencitrate (DAHC) as additive were investigated for ionization of cysteine sulfonic acid-containing peptides in MALDI. A matrix-free ionization method, desorption/ionization on porous silicon (DIOS), was also utilized to evaluate the effect of DAHC. When equimolar three-component mixtures of peptides carrying free cysteine, cysteine sulfonic acid, and carbamidomethyl cysteine were measured by MALDI using a common matrix, alpha-cyano-4-hydroxycinnamic acid (CHCA), no signal corresponding to cysteine sulfonic acid-containing peptide could be observed in the mass spectrum. However, by addition of DAHC to CHCA, the peaks of cysteine sulfonic acid-containing peptides were successfully observed, as well as when using 2,4,6-trihydroxyacetophenone (THAP) and 2,6-dihydroxyacetophenone with DAHC. In the DIOS mass spectra of these analytes, the use of DAHC also enhanced the peak intensity of the cysteine sulfonic acid-containing peptides. On the basis of studies with these model peptides, tryptic digests of oxidized peroxiredoxin 6 were examined as a complex peptide mixture by MALDI and DIOS. In MALDI, the peaks of cysteine sulfonic acid-containing peptides were observed when using THAP/DAHC as the matrix, but this was not so with CHCA. In DIOS, the signal from cysteine sulfonic acid-containing peptides was suppressed; however, the use of DAHC significantly enhanced the signal intensity with an increase in the number of observed peptides and increased signal-to-noise ratio in the DIOS spectra. The results show that DAHC in the matrix or on the DIOS chip decreases discrimination and suppression effects in addition to suppressing alkali-adduct ions, which leads to a beneficial effect on protonation of peptides containing cysteine sulfonic acid.
Kinumi
Tomoya
T
Human Stress Signal Research Center, National Institute of Advanced Industrial Science and Technology, Ikeda, Osaka 563-8577, Japan. t.kinumi@aist.go.jp
Shimomae
Yukiyasu
Y
Arakawa
Ryuichi
R
Tatsu
Yoshiro
Y
Shigeri
Yasushi
Y
Yumoto
Noboru
N
Niki
Etsuo
E
D003545:Cysteine / Q000031:analogs & derivatives* / Q000032:analysis; D005982:Glutathione Transferase / Q000032:analysis; D007834:Lasers; D010446:Peptide Fragments / Q000032:analysis; D010455:Peptides / Q000032:analysis* / Q000138:chemical synthesis; D010544:Peroxidases / Q000737:chemistry; D054465:Peroxiredoxin VI; D054464:Peroxiredoxins; D011492:Protein Hydrolysates; D012825:Silicon; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014357:Trypsin / Q000737:chemistry
D010446:Peptide Fragments; D010455:Peptides; D011492:Protein Hydrolysates; C011119:S-sulphocysteine; D010544:Peroxidases; D054465:Peroxiredoxin VI; D054464:Peroxiredoxins; D005982:Glutathione Transferase; D014357:Trypsin; D003545:Cysteine; D012825:Silicon