HEPATIC TYROSINE-PHOSPHORYLATED PROTEINS IDENTIFIED AND LOCALIZED FOLLOWING IN-VIVO INHIBITION OF PROTEIN-TYROSINE PHOSPHATASES - EFFECTS OF H2O2 AND VANADATE ADMINISTRATION INTO RAT LIVERS

Injection of a combination of H2O2 and vanadate (H/V) into the portal vein of rat livers resulted in inhibition of protein tyrosine phosphat ase activity and led to a dramatic enhanced in vivo protein tyrosine p hosphorylation. Some of the phosphorylated proteins were identified as the beta-subunit of the insulin receptor, the insulin receptor substr ate 1 (pp185), PLC-gamma (pp145), and a 100 kDa PLC-gamma-associated p rotein. Immunofluorescense and immune electron microscopy of frozen li ver sections with anti-P-Tyr antibodies revealed that most of the tyro sine-phosphorylated proteins are localized in close proximity to the p lasma membrane in intercellular adherence junctions and tight junction regions. This close in vivo association between membranal protein tyr osine kinases, their target proteins, and cytoskeletal elements could enable formation of 'signaling complexes' which may play a role in tra nsmembrane signal transduction. By affinity chromatography over immobi lized anti-P-Tyr antibodies, a large number of these tyrosine-phosphor ylated proteins were partially purified.