Many proteins have been identified as candidates for regulation by sulfenic acid formation. However, most of these studies were performed in vitro and in the absence of GSH. Recent literature suggests that although sulfenic acid formation may be the initial oxidative modification for these proteins, S-glutathionylation serves as the more stable intermediate in redox signaling
[9]. This was shown for the molecular chaperone BiP, initially suggested to be regulated by the sulfenic acid formation and later shown to undergo S-glutathionylation through a sulfenic acid intermediate
[10]. Similarly, mammalian protein tyrosine phosphatases (PTPs), initially observed to react with H
2O
2 to form a protein sulfenic acid
[11][12], have been shown to undergo S-glutathionylation in the presence of GSH
[13]. More recently, Heppner et al. showed that the oxidation of epidermal growth factor receptor (EGFR) and non-receptor tyrosine kinase Src by the NADPH oxidase DUOX1 involved sequential oxidation to sulfenic acids and S-glutathionylated proteins
[14]. In agreement with these findings, sulfenic acids have been shown to react much faster with GSH than with oxidants like H
2O
2, thereby escaping further oxidative modification
[15].