Tyrosine and Serine Phosphorylation of Dystrophin and the 58‐kDa Protein in the Postsynaptic Membrane of Torpedo Electric Organ

Abstract: Dystrophin associates with a 58‐kDa and an 87‐kDa protein in the postsynaptic membrane of the Torpedo electric organ. We have previously shown that the 87‐kDa protein is a major phosphotyrosine‐containing protein in these membranes. Immunoprecipitation of the 87‐kDa protein from phosphorylated postsynaptic membranes results in coimmunoprecipitation of additional phosphoproteins. These phosphoproteins are identified as dystrophin and the 58‐kDa protein. Monoclonal antibodies to dystrophin and the 58‐kDa protein immunoprecipitate phosphorylated forms of these proteins from postsynaptic membranes phosphorylated in vitro. Phosphoamino acid analysis reveals that dystrophin and the 58‐kDa protein are phosphorylated on serine and tyrosine residues. In addition, both dystrophin and the 58‐kDa protein are shown to be phosphorylated on tyrosine residues in vivo. These results suggest that the synaptic function of dystrophin and its associated proteins, the 58‐kDa and 87‐kDa proteins, may be modulated by tyrosine and serine protein Phosphorylation.