Abstract
Oxidative inactivation of cysteine-dependent Protein Tyrosine Phosphatases (PTPs) by cellular reactive oxygen species (ROS) plays a critical role in regulating signal transduction in multiple cell types. The phosphatase activity of most PTPs depends upon a 'signature' cysteine residue within the catalytic domain that is maintained in the de-protonated state at physiological pH rendering it susceptible to ROS-mediated oxidation. Direct and indirect techniques for detection of PTP oxidation have been developed (Karisch and Neel, 2013). To detect catalytically active PTPs, cell lysates are treated with iodoacetyl-polyethylene glycol-biotin (IAP-biotin), which irreversibly binds to reduced (S-) cysteine thiols. Irreversible oxidation of SHP-1 after treatment of cells with pervanadate or H2O2 is detected with antibodies specific for the sulfonic acid (SO3H) form of the conserved active site cysteine of PTPs. In this protocol, we describe a method for the detection of the reduced (S-; active) or irreversibly oxidized (SO3H; inactive) form of the hematopoietic PTP SHP-1 in thymocytes, although this method is applicable to any cysteine-dependent PTP in any cell type.