title: GTP binding protein: properties and lack of activation by phosphorylated rhodopsin.
abstract: Taking advantage of the capability of GTP binding protein to bind GTP, we purified the catalytic subunit (G alpha) of bovine rod GTP binding protein by nucleotide-affinity chromatography on Blue Sepharose CL6B. Purified G alpha was essentially free of bound guanine nucleotide and activated by photoactivated rod membranes. Circular dichroism spectra suggested that a significant portion of the protein would be in alpha-helical conformation. No appreciable differences were detected in the circular dichroism spectra when G alpha . GDP and G alpha . GppNp were compared. The extent of G protein activation by rod membranes was reduced moderately by phosphorylation of rhodopsin during photolysis. However, if the pigment had been phosphorylated and regenerated, the ability of rhodopsin to activate G protein was markedly suppressed.
mesh_terms: D000818:Animals; D002417:Cattle; D002942:Circular Dichroism; D004591:Electrophoresis, Polyacrylamide Gel; D005136:Eye Proteins / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006150:Guanine Nucleotides / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism*; D020962:Heterotrimeric GTP-Binding Proteins; D008565:Membrane Proteins / Q000378:metabolism; D010766:Phosphorylation; D012168:Retinal Pigments / Q000494:pharmacology*; D012243:Rhodopsin / Q000494:pharmacology*; D015293:Transducin
chemical_list: D005136:Eye Proteins; C034809:GNAT1 protein, human; D006150:Guanine Nucleotides; D008565:Membrane Proteins; D012168:Retinal Pigments; D006160:Guanosine Triphosphate; D012243:Rhodopsin; D019204:GTP-Binding Proteins; D020962:Heterotrimeric GTP-Binding Proteins; D015293:Transducin