Rhodopsin Phosphorylation Activation

[Orions100]

TL;DR Summary

Is the transition between the two forms of rhodopsin in the retina (that ultimately results in vision) strictly dependent on the frequency/wavelength of light?
Or can the same amount of electromagnetic energy be delivered by convergent radio waves?

While glancing through an ophthalmology textbook several years ago, I learned that the transition between the two forms of rhodopsin (that results in neural activation and, ultimately, vision) can be accomplished through the electromagnetic energy provided by certain radio wave frequencies (and not only light).
(The textbook even included a specific radio wave frequency as an example.)
Is the chemical transition between the two forms of rhodopsin strictly dependent on the frequency and/or wavelength of the incident electromagnetic wave (as most explanations of vision seem to suggest)?
Or is it really only dependent upon receiving the correct amount of energy within the appropriate time frame?
For example …
Can the same transition be accomplished through the use of one or more radio wave signals that converge at an interval equal to the frequency of light?

 

[BillTre]

Visual photoreceptors are known to have fairly wide absorption spectra. They can be activated by a range of different wavelength photons. Here are some examples:

The spectra are adjustable. Evolution has selected in different animals for photopigments best suited for their visual environment.

Its hard to tell what this is about:

(The textbook even included a specific radio wave frequency as an example.)

without more information.

Your combining of alternative wavelengths photons to activate the photoreceptor sounds like how a two photon confocal flourescent microscope works.
The microscope focuses an intense beam of laser photons down to a very small region, such that the photonsensitive compounds are activated by a combination of two (or more) lower energy photons to provide enough energy to activate the molecule. The energies of the photons add up, but not quite in a linear manner.
In this way, lower energy infrared photons, that can penetrate deeper in tissue, can activate photo-sensitive compounds that could not be sufficiently illuminated by the higher energy photons that don't penetrate as well.

Radio frequency waves? I'm thinking not, just because it would seem to require an unrealistic number of simultaneous events (many RF photons) to deliver enough energy.
But I could be wrong.

 

[jim mcnamara]

@BillTre good post.
Microwave frequencies (some) can be absorbed by water. But radio waves like FM and AM transmissions go through man made walls. So your speculation sounds sensible - radio waves are not a very likely candidates. FM wavelengths range from ~1mm to 100km. So if I absolutely had to pick a wavelength I would try some wavelength near 1mm.

 

[Ygggdrasil]

So if I absolutely had to pick a wavelength I would try some wavelength near 1mm.

Opsins respond to light because they contain a chromophore molecule (retinal) that can switch between two different shapes. The amount of energy needed to activate the switch between these two states, is on the order of ~200 kJ/mol, which corresponds to the energy of a visible photon (~500nm). If we want an opsin to be sensitive to microwave frequencies, this transition needs to be caused by the energy associated with a microwave photon (for 1 mm, this corresponds to ~0.1 kJ/mol). This immediately causes a problem because, at human body temperature (37°C, 310K), the amount of thermal energy available is about 2.6 kJ/mol. This means that thermal energy alone will be enough to activate our hypothetical microwave-sensitive opsin! The protein would not actually be able to sense microwaves because it would always be turned on regardless of whether or not microwaves were present.

If you look at calculations like these, you'll see that it is not an accident that animal vision is limited to a small range of the EM spectrum from the near IR to the near UV. This window is determined by the laws of physics. At frequencies significantly below the visible region, you get to the point where thermal energy becomes more energetic than the photons and a chromophore would not be able to distinguish thermal energy from the absorption of photons. At frequencies significantly above the visible region, you get into the range of ionizing radiation, where photons are so energetic that they begin breaking chemical bonds and destroying tissue.

 

[jim mcnamara]

Thanks @Ygggdrasil
I think we both know that radio wavelengths in the context mentioned by another poster is a complete non-starter.

However. Your answer is much better.

 

[Orions100]

How about this.
Would the amount of electromagnetic energy needed to activate the Rhodorsin transition be suitably lowered, if the water molecules that are naturally interspersed with the Rhodopsin were heated up very, very slightly (I.e. through the use of microwaves).

 

[Orions100]

How about this.
Would the amount of electromagnetic energy needed to activate the Rhodorsin transition be suitably lowered, if the water molecules that are naturally interspersed with the Rhodopsin were heated up very, very slightly (I.e. through the use of microwaves).

(Don’t try this at home.)

 

[BillTre]

Don't know about that, but the mechanisms of IR detection in pit vipers (like rattlesnakes) uses a different detection mechanism based on heating:

Molecular mechanism​

In spite of its detection of infrared light, the infrared detection mechanism is not similar to photoreceptors - while photoreceptors detect light via photochemical reactions, the protein in the pits of snakes is a type of transient receptor potential channel, TRPV1 which is a temperature sensitive ion channel. It senses infrared signals through a mechanism involving warming of the pit organ, rather than chemical reaction to light.[12] In structure and function it resembles a biological version of warmth-sensing instrument called a bolometer. This is consistent with the thin pit membrane, which would allow incoming infrared radiation to quickly and precisely warm a given ion channel and trigger a nerve impulse, as well as the vascularization of the pit membrane in order to rapidly cool the ion channel back to its original temperature state. While the molecular precursors of this mechanism are found in other snakes, the protein is both expressed to a much lower degree and is much less sensitive to heat.[12]

The pit organ has no lens and a large opening which would act like a large pinhole. This might generate a rather poorly resolved image.