User:Dudleydoodog/Transducin

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Although the traditional mechanism involves activation of PDE by GTP-bound Tα, GDP-bound Tα has also been demonstrated to have the ability to activate PDE. Experiments of PDE activation in the dark (without the presence of GTP) show small but reproducible PDE activation. This can be explained by the activation of PDE by free GDP-bound Tα. PDE γ subunit affinity for GDP-bound Tα, however, seems to be about 100-fold smaller than for GTP-bound Tα. The mechanism by which GDP-bound Tα activates PDE remains unknown however, it is speculated to be similar to the activation of PDE by GTP-bound Tα. Tα can accelerate the rate of activation of light-off induced Protein Kinase A due to binding to rhodopsin  . '''As well as, transducin achieves full functional activation upon binding to activated rhodopsin. '''

'''There are different isoforms of Tα, seen in rod and cone cells. However, the isoforms exhibit functional interchangeability in the phototransduction cascade and shouldn't solely account for differences in light sensitivity. ''' Although the focus for phototransduction is on Tα, Tβγ is crucial for rhodopsin to bind to transducin. The rhodopsin/Tβγ binding domain contains the amino and carboxyl terminal of the Tα. The amino terminal is the site of interaction for rhodopsin while the carboxyl terminal is that for Tβγ binding. The amino terminal might be anchored or in close proximity to the carboxyl terminal for activation of the transducin molecule by rhodopsin.