Transducin

Transducin is a so-called heterotrimeric G protein, which is found in the photoreceptor cells of the retina. It is an essential part of the visual signal transduction cascade.

A G- protein is composed of three different subunits, which are α, β and γ mentioned. The α - subunit binds inactive GDP state. The activated rhodopsin now initiated the exchange of GDP for GTP on the α subunit of transducin. Thereby disintegrates the transducin in the active α - subunit, the bound GTP and the β - γ subunit. The α subunit then activates the phosphodiesterase ( PDE), by elimination of two inhibitory γ subunits of the PDE. ( Expanded sequence see: Visual signal transduction).

Transducin regenerates itself after some time by themselves by the intrinsic GTPase hydrolyzes the GTP to GDP in the α - subunit. The complex with the γ -PDE decays and α - transducin stores now back with the β - γ subunit together.

Transducin is also involved in the adaptation to the light intensities. Normally, this protein together with rhodopsin in the outer segment of the photoreceptor cell. After prolonged light irradiation of retinal transducin but relocated to the inner segment of the photoreceptor cell. The transport mechanism is still unclear.

• G- protein
• Protein complex