GTP-binding proteins are restricted to signal transduction sites

We have used the Torpedo electric organ to study GTP-binding protein localization since functionally distinct membrane fractions can be isolated from this tissue. Postsynaptic membranes from the innervated face and membranes from the non-innervated face of the electrocyte, as well as presynaptic membranes from the innervating nerve, can be isolated. alpha s was restricted to the innervated face of the postsynaptic cell; alpha i, alpha o, and ras were found only in the presynaptic membrane fraction of the innervating nerve. 21 and 25 kDa GTP-binding proteins were present in all the membrane fractions. These results suggest that specific GTP-binding proteins are differentially restricted to membrane areas specialized in signal transduction.