Membrane-Bound GTP-Transducin Efficiently Activates Retinal cGMP Phosphodiesterase

摘要: Transducin (T, Mr 85,000) is the GTP-binding protein of retinal rod outer segments (ROS) that receives excitation signal from photoisomerized rhodopsin (R*) in first amplified step cyclic GMP cascade vision (1, 2). Transducin, turn, activates a phosphodiesterase (PDE) rapidly hydrolyzes cGMP, leading to closure cGMP-gated channels plasma membrane (for review, see refs. 3–5). R* induces release GDP by transducin, thus catalyzing uptake GTP its subunit (T α -GTP; 39,000); T -GTP then PDE (2). When it binds GTP, disso­ciates β (Mr 35,000) and γ 6,000) subunits transducin βγ ) as well R*.