Transducin
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Transducin (also called Gt) is a heterotrimeric G protein that is naturally expressed in vertebrate retina rods and cones (a different Transducin gene is expressed in each cell type). Heterotrimeric Transducin (alpha-beta-gamma subunits) is activated by a conformational change in rhodopsin due to the adsorption of a photon by rhodopsin's active group retinal; Activation causes the GDP bound to the alpha subunit to be exchanged with GTP from solution and results in activated alpha dissociating from beta-gamma. Active Transducin-alpha then causes cyclic GMP Phosphodiesterase to increase its activity, thereby lowering the concentration of cGMP, an intracellular second-messenger molecule. Decrease in cGMP concentration leads to the closure of cGMP-regulated ion channels and a hyperpolarized membrane potential. This chain of signaling events is also called "the vertebrate phototransduction cascade".
The termination of Transducin activity occurs when (active) GTP bound Transducin is hydrolyzed to Transducin-GDP, a process which is accelerated by a complex containing an RGS (Regulator of G-protein signaling)-protein and the gamma-subunit of the effector, cyclic GMP Phosphodiesterase.
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| This page uses content from the English-language version of Wikipedia. The original article was at Transducin. The list of authors can be seen in the page history. As with Psychology Wiki, the text of Wikipedia is available under the GNU Free Documentation License. |
