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My friend made the claim that there exists a protein in your eye responsible for vision. This protein is sensitive to different wavelengths of light, and when it gets hit by the right wavelength, it kinks. In order to be un-kinked, he claimed, it has to be shipped down to the liver, and then back up to the eye.

He teaches organic chemistry at UCLA, so I trust him a little bit. But I couldn't find this with a quick search. Anyone know if this is legit?

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    $\begingroup$ Luckily, the unkinking can happen outside of the liver, and much quicker. You know how, if somebody suddenly shines a flashlight into your eyes, you go blind for a couple of seconds after the light is gone? The reason is that all your protein storage in the eye is already activated and needs to be brought back to the unkinked state before you can see again. Imagine how it would be if this process required several heartbeats for transport to the liver, then an enzymatic process straightening the kinks, than shipping back: the blinding will be longer by at least one order of magnitude. $\endgroup$
    – rumtscho
    Apr 21, 2014 at 15:36

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The protein is called rhodopsin and the bit that gets kinked up is called retinol. Normally when light hits it, it does trans to cis isomerization at the 11th carbon. 'kinks up' is a pretty apt way of describing it.

enter image description here

I'm not familiar with the shipped down to the liver part, but I'm guessing that the photo reaction of the retinol with itself or the protein must occasionally make the rhodopsin-retinol complex unfunctional - perhaps by the double bonds cross linking to other atoms in the retinol or to the protein. As I understood it the retinol just straightens out again. This reference shows that in the presence of rhodopsin, 11-cis retinol will become all trans again normally.

There should be enzymes in the liver that can recycle some messed up retinol configurations. Its probably not the main route through your body. Retinol is stored in the liver from dietary intake, and then shipped via retinol binding proteins to the eye. So that is the organ which is the source of retinol in the human body (and probably most animals). It should catch damaged retinols and refurbish them the same way it does those taken in via the diet.

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