Detection of cyclic GMP binding protein and ion channel activity in frog rod outer segments.
In order to identify the cGMP-sensitive ion channel protein in frog rod outer segments (ROS), we analyzed cGMP binding proteins in the ROS by means of photoaffinity labeling with [3H]cGMP. We found four cGMP binding proteins with molecular weights (Mws) of 250K, 100K, 92K, and 53K. The 250K protein was an integral-membrane protein, which we named cG-Protein, (cG stands for cGMP). The cGMP-binding to cG-Protein was slightly increased by CaCl2. cG-Protein has a carbohydrate moiety. The amount of cG-Protein per single rod outer segment was estimated to be 9.0 x 10(6) molecules. Light-dependent phosphorylation of cG-Protein with [gamma-32P]ATP was observed. The 100K and 92K proteins were peripheral-membrane proteins, corresponding to cGMP phosphodiesterase. The 53K protein was a soluble protein. Incorporation of a membrane protein fraction of frog ROS into a planar lipid bilayer resulted in the appearance of at least three kinds of ion channel activities; two of them were related to cGMP. The possibility that cG-Protein is the cGMP-sensitive ion channel in vivo is discussed.
D000818:Animals; D002352:Carrier Proteins / Q000302:isolation & purification / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D007473:Ion Channels / Q000378:metabolism* / Q000502:physiology; D008027:Light; D008051:Lipid Bilayers; D008564:Membrane Potentials; D008970:Molecular Weight; D010766:Phosphorylation; D010786:Photoreceptor Cells / Q000378:metabolism*; D011892:Rana catesbeiana; D012374:Rod Cell Outer Segment / Q000378:metabolism*
D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D007473:Ion Channels; D008051:Lipid Bilayers; C022994:cyclic GMP-binding protein; D006152:Cyclic GMP