Identification of GTP-binding proteins in myelin and oligodendrocyte membranes

Myelin membranes purified from mouse and rat brain are associated with alpha subunits of four signal transducing guanosine triphosphate (GTP)-binding proteins: Go, Gi, Gs, and ras. Four low-molecular-weight (Mr) GTP-binding proteins are also present, as demonstrated by the binding of GTP to proteins immobilized in nitrocellulose. This latter group is more prominent at early stages of myelination and remains associated with isolated myelin membranes despite repetitive cycles of purification. At least one nonmyelin subcellular membrane fraction possesses the same proteins. The total membrane fraction of cultured oligodendrocytes is associated with both groups of GTP-binding proteins. None of the well-known myelin proteins bound GTP by the procedure described.