Identification of a rabphilin-3A-interacting protein as GTP cyclohydrolase I in PC12 cells

Rabphilin-3A is a putative target protein for Rab3A small GTP-binding protein which is implicated in neurotransmitter release. To identify a Rabphilin-3A-interacting protein, proteins were immunoprecipitated by an anti-Rabphilin-3A polyclonal antibody from the lysate of PC12 cells and subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis followed by protein staining. Several proteins were coimmunoprecipitated with Rabphilin-3A and one of these proteins with a M(r) of about 30 KDa was phosphorylated in intact PC12 cells stimulated by high KCl. The amino acid sequence analysis of this 30 KDa protein revealed that it is GTP cyclohydrolase I.