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Published July 16, 2009 | Supplemental Material
Journal Article Open

Simultaneous Detection of Cysteine Sulfenate, Sulfinate, and Sulfonate during Cysteine Interfacial Ozonolysis


Sulfenic acids (RSOH) are reactive intermediates in the oxidation of protein cysteines. Among cysteine oxoforms, RSOH represent redox-reversible species that can thus participate in regulation and signaling mechanisms and play key roles in enzyme catalysis and antioxidant activity. How the cysteine (CyS) thiol groups of the human surfactant protein that lines the lung epithelium react with inhaled ozone is deemed critical in preserving structural integrity and immune functions. Here we report the simultaneous detection, by online thermospray ionization mass spectrometry, of cysteine sulfenate (CySO^−) and the overoxidized cysteine sulfinate (CySO_2^−) and cysteine sulfonate (CySO_3^−) species on the surface of aqueous CyS microdroplets exposed to O_3(g) for <1 ms. These species are produced by rapid, sequential O-atom additions whose relative rates are herein quantified for the first time. From the pH-dependence of ozonation rates, we derive pK_a(CySOH) = 7.6 ± 0.3 < pKa(CyS) = 8.3.

Additional Information

Copyright © 2009 American Chemical Society. Received: May 8, 2009; Revised Manuscript Received: June 9, 2009. Publication Date (Web): June 18, 2009. S.E. thanks the Japan Society for the Promotion of Sciences Postdoctoral Fellowship for Research Abroad. This project was supported by the National Science Foundation (ATM-0714329).

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