Regulation of Ca2+/calmodulin-dependent protein kinase phosphatase (CaMKP) by oxidation/reduction at Cys-359

► CaMKP was inactivated by oxidation with H2O2 or by alkylation with iodoacetamide. ► Oxidized CaMKP was reactivated by incubation with reducing agent 2-mercaptoethanol. ► Human CaMKP (hCaMKP) has three Cys residues, Cys-259, Cys-315 and Cys-359. ► A disulfide bond between Cys-359 and Cys-259/Cys-315 was formed upon oxidation. ► hCaMKP activity is reversibly regulated by oxidation/reduction at Cys-359.