Neuropeptide Y promotes GTP photo-incorporation into a 55 kDa protein

Incubation of bovine hippocampal membranes with [α-³²P]GTP and exposure to ultraviolet light resulted in the labelling of seven species with apparent molecular masses of 200, 74, 55, 53, 50, 43 and 40 kDa. Labelling of the 55 kDa species was greatly enhanced in the presence of carboxyl terminal fragments [neuropeptide Y-(18-36)] of neuropeptide Y. Labelling occurred with [α-³²P]GTP but not [α-³²P]ATP. A group of putative direct G protein activating peptides including mastoparan, melittin, substance P and adrenocorticotropic hormone (ACTH)-(1-24), were also able to stimulate the labelling of this protein. Labelling of the 55 kDa protein could be demonstrated in bovine brain but not peripheral tissues. Western blot analysis using an antibody against the common α subunit of G proteins recognized a protein co-migrating with the 55 kDa GTP-binding protein. These findings demonstrate the existence of a previously uncharacterized neuronal protein, with an apparent molecular mass of 55 kDa, that binds GTP in response to neuropeptide Y and other peptides.