Which of the following G-protein takes part in the regulation of vision?

(a) Golf

(b) Gi family

(c) Gs family

(d) Gq family

The correct answer is (b) Gi family.

The specific G-protein involved in the regulation of vision in vertebrates is called transducin (often abbreviated as Gₜ). Transducin is a key member of the Gαi subfamily, which is part of the larger Gi family of G-proteins.

The Role of Transducin in Vision

The process of vision begins in the photoreceptor cells (rods and cones) of the retina. Here's a simplified breakdown of the signaling cascade: 

1. Light Activation: A photon of light is absorbed by the retinal molecule within the rhodopsin protein (a G-protein-coupled receptor).This causes retinal to change shape, activating rhodopsin.
2. G-Protein Activation: The activated rhodopsin then activates hundreds of transducin (Gₜ) molecules.
3. Enzyme Activation: Each activated transducin molecule, in turn, activates an enzyme called phosphodiesterase (PDE).
4. Second Messenger Breakdown: PDE rapidly breaks down a second messenger molecule called cyclic GMP (cGMP) into GMP.
5. Channel Closing & Signal: The sharp drop in cGMP concentration causes ion channels in the cell membrane to close. This closure changes the electrical state of the cell (hyperpolarization), which is the signal that is ultimately transmitted to the brain and interpreted as light.