Table 1 Oxidation forms of protein cysteines
Oxidation productNotesReversibility
Free thiol (SH)
Intraprotein disulphides (SS)Thioredoxin
Interprotein disulphides (SS)Thioredoxin
Mixed disulphides (SS)Glutathionylation (PSSG); cysteinylationGlutaredoxin and thioredoxin; GSH
S-nitrosothiols (SNO)Glutaredoxin, thioredoxin and ascorbate
Sulphenic acids (SOH)Easily reduced by GSH or thioredoxin [37]
Sulphinic acids (SO2H)Can be reduced by thioredoxin [20], but this is debated and it was suggested that only sulphiredoxin does it [38]
Sulphonic acids (SO3H)Irreversible