Odorant molecules signal the G-protein receptors with their unique IR spectra

Sept. 26, 2010 - PRLog -- Background

Olfaction by shape and vibration mechanisms that claim to explain smell has a long history of controversy.

Shape Mechanism The olfaction shape mechanism was formulated in 1949 based on Linus Pauling's notion of shape-based molecular interactions. The shape mechanism superseded the vibration theory of olfaction and today remains the mainstream theory. When Linda Buck and Richard Axel published their Nobel Prize winning research on the olfactory receptors in 1991, the G-protein receptors were used for olfaction. Since all types of G-protein receptors currently known are activated through binding of molecules with highly specific conformations, or shape, it was assumed that olfactory receptors operate in a similar fashion. Current work on shape theory focuses on neural processing, rather than the specific interaction between odorant and receptor that generates the original signal See. http://en.wikipedia.org/wiki/Shape_theory_of_olfaction

Vibration Mechanism The vibration mechanism was first proposed in 1937 after which it was largely abandoned in favor of the competing shape theory. A 1996 paper by Luca Turin revived the theory by proposing a mechanism, speculating that the G-protein-coupled receptors were actually measuring molecular vibrations using inelastic electron tunneling, rather than responding to Pauling’s molecular keys that work by shape alone.

By the vibration mechanism, the odor character is encoded in the receptors tuned to different vibration frequencies. Although the vibration mechanism explains odor character, it does not explain intensity, i.e., why some odors are stronger than others at the same concentrations. Also, it may be argued the relation between vibration frequencies and odor is not causal, but may come about indirectly as a consequence of similar molecules having similar properties such as in Cheminformatics, in which a variety of approaches are used to predict the function of molecules from their characteristics See http://en.wikipedia.org/wiki/Vibration_theory_of_olfaction

Problems
Both shape and vibration mechanisms have a fundamental problem. Both lack a source of EM energy to to signal the G-protein receptor that the odorant molecule is in the nose. EM stands for electromagnetic. For example, EM energy in the form of infrared (IR) laser radiation could, if available excite the odorant molecule to emit its spectral content as the signal for G-protein recognition. Moreover, the odorant molecule must first fit in the receptors’ binding site. But this process if left to chance requires time consuming trial and error procedures. The vibration mechanism not only must follow the shape mechanism in this regard, but must have a vibration energy mode compatible with the difference in energies between two energy levels on the receptor, so electrons can travel through the molecule via inelastic electron tunneling. Neither shape nor vibration mechanisms as they now stand can be the mechanism nature intended for the nose to smell. But Nature has provided every atom in our body with thermal kT energy. Here, k is Boltzmann’s constant and T absolute temperature.

QED induced Radiation Mechanism
The QED induced radiation mechanism uses the kT energy of atoms in the epithelial layer of the nose as the EM energy source that by QM excites the colliding odorant molecule to emit its spectra as the signal to the G-receptor. QED stands for quantum electrodynamics and QM for quantum mechanics. QED induced radiation was developed [1] for nanoparticles (NPs) that by QM have zero specific heat. Any EM energy absorbed by NPs therefore cannot be conserved by an increase in temperature, and instead is emitted as QED radiation at the total internal reflection (TIR) resonance of the NP.

Odorant molecules may be considered small NPs. But a molecule does not have a TIR resonance – only vibration resonances represented by its IR spectra. Nevertheless, QED radiation like a laser excites the odorant molecule to emit its unique IR spectra. Prior to collision, the temperature of the odorant molecule in the ambient air is near 20 C while the nose is at body temperature of about 37 C. The odorant molecule therefore absorbs thermal kT energy upon collision. Upon breaking contact with the nose surface, the odorant molecule by QM cannot conserve the absorbed kT energy by an increase in temperature, and therefore conservatrion proceeds by the emission of non-thermal QED induced radiation given by its IR spectra. The odorant molecule by emitting its unique IR spectra therefore signals the G-protein that it alone is present inside the nose.  

Discussion

Shape Mechanism  Olfactory receptors need not be activated through binding of molecules with highly specific shape, although contact is required in the QED mechanism to absorb kT energy from the receptor. Of a more fundamental significance, Pauling’s long standing shape-based molecular interactions are placed in question.

Vibration Mechanism Luca Turin’s argument that the G-protein-coupled receptors discovered were actually measuring molecular vibrations, rather than responding to molecular keys that work by shape may be extended to the IR spectra signal of the odorant molecule by QED induced radiation. QM is involved, but not through the complex [2] phonon assisted electron tunneling. QED induced IR spectra is a far more credible QM mechanism. The IR spectra from the odorant molecule will produce its own electrons in the appropriate G-protein receptor by the photoelectric effect. QED induced radiation spectra is the same as Turin’s odor character encoded in receptors tuned to different vibration frequencies, but differs in that the absorption of the odorant molecule to thermal kT energy explains why some odors are stronger than others at the same concentrations. Given that the IR spectra of the odorant molecule is uniquely defined by QED induced radiation, a causal relationship with odor is very likely.

QED Induced IR Spectra  Unlike QED induced radiation, both shape and vibration mechanisms lack a a source of EM energy for activation. Lock and key models rely [2] on docking for discrimination, and mechanical mechanisms for actuation, but the source of the charge is not defined. Similarly, the vibration mechanism requires a source of electrons or holes to allow charge flow to take place, but the precise biological origin is not known.

However, QED radiations require that the odorant molecule absorb EM energy in collisions, and therefore the efficiency of the odorant molecule absorbing kT energy prior to breaking contact is important. Momentary collisions limit the efficiency of kT energy absorbed by the odorant molecule, but can be improved by extending the contact time, say by the viscous mucous layer covering the epithelial surface. Indeed, the importance of contact time is consistent with the improved performance of artificial electronic nose devices from polymer coatings that mimic the action of snot in the natural nose. See http://news.bbc.co.uk/2/hi/technology/6614567.stm

Conclusions

The QED induced IR spectra of the odorant molecule signals the G-protein receptor of its presence.

Both shape and vibration mechanism of olfaction that are based on contact of the odorant molecule with the epithelial layer of the nose are superseded by the QED induced IR spectra mechanism.

The property of an odorant molecule that the G-protein receptors in our nose pick up is proposed to be the unique IR spectra of the odorant molecule.

References
1.  Prevenslik, T.  See http://www.nanoqed.org
2.  Brookes, J. et al., “Could Humans Recognize Odor by Phonon Assisted Tunneling?”, PRL, 98, 038101, 2007.

# # #

About QED Indcued EM Radiation: Classically, absorbed EM energy is conserved by an increase in temperature. But at the nanoscale, temperature increases are forbidden by quantum mechanics. QED radiation explains how absorbed EM energy is conserved at the nanoscale by the emission of nonthermal EM radiation