Taste molecules

The dipeptide L-aspartyl-L-phenylalanine methyl ester (aspartamine) is about 200 times sweeter than sucrose. From conformational studies of this peptide and its derivatives, employing NMR, X-ray crystallography, and molecular modeling techniques, Goodman et at the University of Califor- 

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Sensory receptors expressed in particular in taste receptor cells of the taste buds that sense the five basic tastes salt, sour, sweet, bitter and umami (glutamate taste). Sodium type ion channels sense salty taste whereas sour taste is transduced by potassium type ion channels. The underlying cause of sweet, bitter, and umami tastes is the selective activation of different groups of G protein coupled receptors that discriminate between sweet, bitter, and umami tasting molecules. 

Fig. 11.—Identity of the Third Structural Feature Comprising the Postulated Glucophore in Some Sweet-tasting Molecules. ...

Sweet-tasting molecule (S) binds to sweet-taste receptor (SR), activating the G protein gustducin (Ggust). 

We know that binding between stimulus and receptor is a weak one because no irreversible effects have been observed. A mechanism of taste stimulation with electrolytes has been proposed by Beidler (1957) it is shown in Figure 7-3. The time required for taste response to take place is in the order of 25 milliseconds. The taste molecule is weakly adsorbed, thereby creating a disturbance in the molecular geography of the surface and allowing an interchange of ions across the surface. This reaction is followed by an electrical depolarization that initiates a nerve impulse. 

Grigorov, M.G., SchUchtherle-Cerny, H., Affolter, M., Kochhar, S., Design of virtual libraries of umami-tasting molecules. J. Chem. Inform. Comp. Sd. 43, 1248-1258 (2003)... 

Bassoli, A., Drew, M.G.B., Merlini, L., and Morini, G. (2002a). A general pseudoreceptor model for sweet compounds, semi-quantitative prediction of binding affinity for sweet tasting molecules. J. Med. Chem. 45, 4402—1409. 

D-form Amino acids tend to taste sweet, whereas L-forms are usually tasteless. This is again due to our chiral taste molecules. The smells of oranges and lemons are examples of the D and L enantiomers. 

The latest model for the sweet-taste receptor, proposed by Piero Temussi of the University of Naples, postulates that there are four binding sites on the receptor that can be occupied independently. Small sweet-tasting molecules might bind to one of the sites, while a large molecule would bind to more than one site simultaneously. 

Other hand, TasteDB spans a broader range of SMIfjp values, in particular, mai taste molecules contain a large number of aromatic carbon atoms. 

Figure 5.3. Sweet tasting molecules showing the AH-B-X groups postulated by Shallen-berger-Kier hypothesis. The numbers in parenthesis are the degrees of sweetness relative to sucrose.

One important point on smell is that just as with taste molecules of different structures, often totally different molecules, have the same or different smell. An example of rose odor in reference (1.) sites the work of Wright (12) where rosetone, phenylethanol, geraniol and pelargol are compounds with very different structures but the same smell. He also attributes camphor smell to camphor, chloroethane and ethyl-tert-butyl ether (12). Other research of this type would be odorant molecules of similar structure with a different olfactory response. In 1929 Braun (13) studied a series of ketones where the carbonyl moved from carbon two through carbon six of an eleven carbon ketone. 

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