Odorant interaction, receptor site

Section 7 8 Both enantiomers of the same substance are identical m most of then-physical properties The most prominent differences are biological ones such as taste and odor m which the substance interacts with a chiral receptor site m a living system Enantiomers also have important conse quences m medicine m which the two enantiomeric forms of a drug can have much different effects on a patient... 

Most, perhaps all of the odor theories advanced so far made the assumption that the transcription of structureil information encoded in the stimulant molecule into an odor information pattern is an integral process One odorivector (AMOORE, 2) interacts with one receptor site and this interaction resvilts in transcription of all structural components simviltaneously into their corresponding informational modalities. However, observation tells us that olfactory information is inherently complex Ambergris for instance is described (OHLOFF, 3) by six distinctly different notes. This would imply that in an integral process of the periphersil molecular interaction one single neuron has to detect at least six different profiles with six different receptor sites and project the informational modalities intact to the higher centers. 

That this peripheral interaction of odorivectors is a reality and not Just a postulate resulting from lengthy speculations has been confirmed by statistically significant experimental proof obtained in malodor/"antlmalodor"-interaction studies (l ), and on a more general base, in odor/odor-interactions. These resiolts give implicit proof that specific receptor sites for moleciLLar and active profiles exist. 

The above interpretations of the data do not consider the alternative implications of a multiple receptor site model for the odorant-receptor Interaction. In such a model the response elicited by a ligand results from the simultaneous binding of several groups rather than one. Thus if one group is modified it may alter the odorant molecule in such a way that it no longer binds to other sites contributing to the response. 

Figure 15.8 Schematic representation of the proposed mechanisms for mode of action of OBPs in the perireceptor events. Pheromone (or other semiochemicals) enters the sensillar lymph through cuticular openings (pore tubules), is solubilized by an odorant-binding protein, transported to the olfactory receptors, and protected from degrading enzymes. Interaction with negatively charged sites at the surface of the dendrites triggers a conformational change that leads to the formation of a C-terminal a-helix. The insertion of this helix into the binding cavity ejects the pheromone to the olfactory receptors.

A consistent feature exists in all of these models, in that, for a good odorant/receptor fit, each model requires a polar group in the odorant that can form a hydrogen bond or similar interaction with a donor site in the receptor and the rest of the fit is determined by a spatial match with the shape of the... 

---