May regulate the activity of several effector molecules involved in synaptic plasticity and neuronal cell survival, including MAPKs, Src family kinases and NMDA receptors. H2O + O-phospho-L-tyrosyl-[protein] = L-tyrosyl-[protein] + phosphate Additional isoforms seem to exist. STEP20 is expressed only in the CNS. Phosphorylation at Ser-221 by PKA deactivates PTPN5. Phosphorylation at Thr-231 and Ser-244 by MAPKs stabilizes the phosphatase, dephosphorylation of these sites results in ubiquitin-mediated degradation of the active phosphatase (By similarity). Lacks the catalytic domain. Lacks the catalytic domain. Belongs to the protein-tyrosine phosphatase family. Non-receptor class subfamily.