title: Characterization of substrate specificity of the protein tyrosine phosphatase purified from the electric organ of Torpedo californica.
abstract: The nicotinic receptor is highly phosphorylated on tyrosine residues both in vivo and in vitro. Tyrosine phosphorylation has been shown to regulate the functional properties of the receptor. We have purified a protein tyrosine phosphatase from the electric organ of Torpedo californica that dephosphorylates the nicotinic receptor. The unique biochemical properties of the purified enzyme suggest that it may be a novel phosphotyrosine protein phosphatase. In this report, substrate specificity of the protein purified from T. californica was characterized using four different tyrosine-phosphorylated substrate proteins. In addition to the nicotinic receptor, the Torpedo phosphatase dephosphorylated insulin receptor and Reduced Carboxamidomethylated and Meleylated lysozyme (RCM lysozyme), however, at a rate much slower than for the nicotinic receptor. In contrast, it appeared to have no effect on the phosphotyrosine level of pp15, a fatty acid binding protein (O-phospho-tyr19-422/aP2) phosphorylated by insulin receptor kinase in 3T3-L1 adipocytes. Interestingly, a protein tyrosine phosphatase (HA1) purified from adipocyte dephosphorylated both nicotinic receptor and pp15 at a similar rate. These results suggest that the Torpedo protein tyrosine phosphatase is relatively specific for the nicotinic receptor.
authors.affiliation: Department of Neuroscience, Howard Hughes Medical Institute, Johns Hopkins University School of Medicine, Baltimore, MD 21205-2185.
authors.forename: L
authors.initials: L
authors.lastname: Mei
authors.forename: K
authors.initials: K
authors.lastname: Liao
authors.forename: R L
authors.initials: RL
authors.lastname: Huganir
mesh_terms: D000818:Animals; D001345:Autoradiography; D002352:Carrier Proteins / Q000378:metabolism; D004557:Electric Organ / Q000737:chemistry*; D050556:Fatty Acid-Binding Proteins; D006868:Hydrolysis; D009113:Muramidase / Q000378:metabolism; D009363:Neoplasm Proteins; D010766:Phosphorylation; D017027:Protein Tyrosine Phosphatases / Q000302:isolation & purification* / Q000378:metabolism; D011972:Receptor, Insulin / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000378:metabolism; D013379:Substrate Specificity; D013997:Time Factors; D014101:Torpedo
chemical_list: D002352:Carrier Proteins; D050556:Fatty Acid-Binding Proteins; D009363:Neoplasm Proteins; D011978:Receptors, Nicotinic; D011972:Receptor, Insulin; D017027:Protein Tyrosine Phosphatases; D009113:Muramidase