Can retinal emit as well as absorb photons?

Y

Yamayama

Registered Senior Member
Retinal: the molecules which absorb photons of light in the photoreceptors at the back of our eyes; they combine with an opsin molecule to form photopigments.

It seems to me that: just as isomerization of retinal from 11-cis-retinal to all-trans-retinal corresponds to the absorption of a photon, changing back from all-trans-retinol to 11-cis-retinol - which is a necessary step for rhodopsin regeneration - surely corresponds to the emission of a photon.

If my suspicion is correct, I guess the reason this isn't observed is because rhodopsin regeneration occurs in the RPE (retinal pigmented epithelium, which is high in melanin - fantastic for absorbing light).

Can anyone affirm/disaffirm my suspicions?
 
The switch from cis to trans configuration release some of the acquired energy to the rhodopsin molecule inducing a conformational change, which then set off that energy in a chemical pathway. Which eventually leads to ion depolarization of the membrane of the rod or cone cell and firing off of a neuron. Because not all the energy required to switch cis to trans was stored perhaps retinal when releasing its energy by switching back from trans to cis emits light at below optical frequencies (IR)?

The energy from trans-retinal is usually used by the cell not re-emitted as light but for biochemcal nergy. Cyanobacteria use retinal to make ATP. I guess hypothetically that a enzyme could exist for switching retinal from trans to cis to produce light and for imputing energy to make trans-retinal, perhaps some forms of life do this for bioluminescence.
 
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Ah, yes, of course. The energy of the photon emitted (if one is emitted) might not necessarily be in the visual range. Didn't even occur to me.

The process of rhodopsin regeneration isn't fully understood yet, as far as I know (could be wrong), and the sequence of reactions is somewhat complex I would imagine.

I'll have to look into it some more.

Thanks
 
That's actually a very informative link, and answers other questions I have about the beginning stages of the visual system.

Thanks again
 
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