As a G protein, it consists of three different subunits called α, β and γ. The α-subunit binds GDP in the inactive state . The activated rhodopsin now initiates the exchange of GDP for GTP on the α-subunit of the transducin. This breaks down the transducin into the active α-subunit that has bound GTP and the β-γ-subunit. The α-subunit now activates the phosphodiesterase (PDE) by splitting off two inhibitory γ-subunits of the PDE. (For a detailed procedure, see: Visual signal transduction ).
Transducin regenerates itself after some time by the intrinsic GTPase in the α-subunit hydrolyzing the GTP in GDP. The complex with the γ-PDE breaks down and α-transducin now reassembles with the β-γ subunit.
Transducin is also involved in the adaptation to light intensities. Usually this protein is found together with rhodopsin in the outer segment of the photoreceptor cell . However, after prolonged exposure of the retina to light, transducin is shifted to the inner segment of the photoreceptor cell . The transport mechanism is still unclear.
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