May play a role in the regulation of T and B-lymphocyte development and signal transduction. H2O + O-phospho-L-tyrosyl-[protein] = L-tyrosyl-[protein] + phosphate Inhibited upon FCER1A triggering. Oxidized form is preferentially associated with actin cytoskeleton. Expressed in bone marrow-derived mast cells. Oxidized at active site cysteine. Treatment with pervanadate (vanadate and H(2)O(2)) or with antigen enhanced oxidation of active site cysteine. Belongs to the protein-tyrosine phosphatase family. Non-receptor class subfamily.