Formation and functions of protein sulfenic acids.

Protein sulfenic acids are generated as reversibly oxidized cysteinyl residues formed upon reaction of thiols with peroxides, nitric oxide, peroxynitrite, and other reactive oxygen or nitrogen species. They can be stabilized within the protein environment, irreversibly oxidized to sulfinic and sulfonic acids by additional oxidant, condensed with protein or exogenous thiol groups to form disulfide bonds, or directly reduced back to thiols. Sulfenic acids in proteins can act as intermediates in redox catalysis or as critical components in cysteine-dependent redox regulation.