Analytical Sciences

Desorption/Ionization Efficiency of Peptides Containing Disulfide Bonds in Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry

Yasushi SHIGERI,* Satoshi INAZUMI,** Yoshihisa HAGIHARA,* Akikazu YASUDA,* Hideya KAWASAKI,** Ryuichi ARAKAWA,** and Makoto NAKATA***

*Health Research Institute, National Institute of Advanced Industrial Science and Technology, 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan
**Department of Chemistry and Materials Engineering, Kansai University, Suita, Osaka 564-8680, Japan
***SAITO Research Center, Peptide Institute, Inc., 7-2-9 Saito-Asagi, Ibaraki, Osaka 567-0085, Japan

In order to elucidate the role of desorption/ionization efficiency of peptides in MALDI-MS, we focused on peptides with disulfide bonds, which form a rigid tertiary structure. We synthesized seven sets of peptides with one disulfide bond (oxytocin, somatostatin, [Arg⁸]-vasopressin, [Arg⁸]-vasotocin, cortistatin, melanin-concentrating hormone, urotensin II-related peptide) and five sets of peptides with two disulfide bonds (tertiapin, α-conotoxin GI, α-conotoxin ImI, α-conotoxin MI and α-conotoxin SI). Each peptide set consisted of three peptides: the oxidized form (S-S type), the reduced form (SH type), and an internal standard peptide in which all cysteine residues were substituted with alanine residues. In the case of urotensin II-related peptide, tertiapin, α-conotoxin ImI and α-conotoxin MI, the reduced form showed higher desorption/ionization efficiency than the oxidized form. In contrast, the other peptides revealed higher desorption/ionization efficiency in the oxidized form relative to the reduced form. These results imply that a rigid structure of peptides formed by disulfide bonds does not correlate with desorption/ionization efficiency in MALDI-MS.

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