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The release of neurotransmiter is regulated in the processes of membrane docking and membrane fusion between synaptic vesicles and presynaptic plasma membranes. Synaptic vesicles contain a diverse set of proteins that participate in these processes. Small GTP-binding proteins exist in the synaptic vesicles and are sugested to play roles for the regulation of neurotransmiter release. We have examined a possible role of GTP-binding proteins in the regulation of protein phosphory-lation in the synaptic vesicles. GTPγS stimulated the phosphorylation of 46 kDa protein (p46) with pI value of 5.0-5.2, but GDPβS did not. The p46 was identified as protein interacting with C-kinase 1 (PICK-1) by MALDI-TOF mass spectroscopy an-alysis, and anti-PICK-1 antibody recognized the p46 spot on 2-dimensional gel electrophoresis. Rab guanine nucleotide dissociation inhibitor (RabGDI), which dissociates Rab proteins from SVs, did not affect phosphorylation of p46. Ca2+/ calmodulin (CaM), which causes the smal GTP- binding proteins like Rab3A and RalA to diso-ciate from the membranes and stimulates CaM- dependnet protein kinase(s) and phosphatase, the presence of cyclosporin A and cyclophylin. However, RhoGDI, which dissociates Rho proteins from membranes, reduced the phosphorylation of p46 to the extent of about 50%. These results support that p46 was PICK-1, and its phosphory-lation was stimulated by GTP and Ca2+/CaM di-rectly or indirectly through GTP-binding protein(s) and Ca2+/CaM efector protein(s). The phosphoryl-ation of p46 (PICK-1) by GTP and Ca2+/CaM may be important for the regulation of transporters and neurosecretion.calcium; calmodulin; guanosine triphos-phate; phosphorylation; rho GTP-binding proteins; syn-aptic vesicles
