Phototransduction

I'm assuming guanylate cyclase.

Thank. You guys are awsome!

Is that the actual answer?

I need this too lol

This is what I found out after some research:

Once the light goes off again, Guanylate Cyclase Activating Protein  interacts with Guanylate cyclase activating it. Guanylate Cyclase Activating Protein (GCAP) is a calcium binding protein, and as the calcium levels in the cell have decreased, GCAP dissociates from its bound calcium ions, and interacts with Guanylate Cyclase, activating it. Guanylate Cyclase then proceeds to transform GTP to cGMP, replenishing the cell's cGMP levels and thus reopening the sodium channels that were closed during phototransduction .