title: A GTP-protein activator of phosphodiesterase which forms in response to bleached rhodopsin.
abstract: A specific protein associated with rod-outer-segment disc membranes binds GTP only in the presence of bleached rhodopsin. Once formed the protein-GTP complex becomes a soluble activator of cGMP phosphodiesterase. It is shown that this activator complex can be completely separated from rhodopsin and retain its ability to activate phosphodiesterase when added to a pool of totally dark (unilluminated) disc membranes. The photoreactive GTP analogue p3-(4-azidoanilido)-5' GTP (AAGTP) is shown to be a more effective substrate than GTP, Gpp(NH)p or 8-azido GTP. [8, 5' 3H] AAGTP was used to specifically covalently label the GTP-binding protein. The protein labeled exhibits a mass of 40,000 daltons when analyzed by SDS-PAGE.
mesh_terms: D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000378:metabolism*; D000345:Affinity Labels; D000818:Animals; D004789:Enzyme Activation; D005136:Eye Proteins / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism*; D066298:In Vitro Techniques; D008027:Light; D008970:Molecular Weight; D011892:Rana catesbeiana; D012168:Retinal Pigments / Q000378:metabolism*; D012243:Rhodopsin / Q000378:metabolism*; D012374:Rod Cell Outer Segment / Q000378:metabolism
chemical_list: D000345:Affinity Labels; D005136:Eye Proteins; D012168:Retinal Pigments; D006160:Guanosine Triphosphate; D012243:Rhodopsin; D015106:3',5'-Cyclic-GMP Phosphodiesterases