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 Phosphorylation at Ser-245 by PKA deactivates PTPN5. Phosphorylation at Thr-255 and Ser-268 by MAPKs stabilizes the phosphatase, dephosphorylation of these sites results in ubiquitin-mediated degradation of the active phosphatase. Belongs to the protein-tyrosine phosphatase family. Non-receptor class subfamily. It is uncertain whether Met-1 or Met-25 is the initiator.