Sweet taste mechanism

An alternative view (123) is that no single model can adequately explain why any given compound is sweet. This hypothesis derives from several features. First, there is the observation that all carbohydrates having a critical ratio of OH to C are sweet tasting. In other words, there are no stmctural constraints to the sweetness of carbohydrates. Second, not all sweeteners can be fit to the same SAR model. Rather, some fit one, others fit another. Third, studies on the transduction mechanisms of sweetness suggest more than a single mechanism for sweet taste, implying multiple receptors for sweeteners. 

The great dependence of taste on hydrophobicity was quantitatively demonstrated by Deutsch and Hansch. From the bulk of the evidence available, they reasoned that the mechanism of sweet-taste stimulation is probably not very different from the mode of action of drugs. 

Margolskee, R. F. Molecular mechanisms of bitter and sweet taste transduction. /. Biol. Chem. 277 1-4, 2002. 

Sweet taste receptor, 24 246-247 identification of, 24 248 Sweet-taste transduction mechanisms,... 

The sweet taste and olfactory responses to a variety of stimuli are examples of chemical senses that utilize protein receptors for initial detection of the stimulus. Most bitter compounds have a hydrophobic component which enables their direct interaction with the cell membrane however, some evidence suggests a protein receptor mechanism. The cooling sensation is treated as a chemesthetic sense, where stimulation takes place at the basal membrane. However, compounds that evoke this response have very specific structural limitations, and most are related to menthol. For purposes of discussion, bitter and cooling sensations will be discussed under generalized receptor mechanisms. 

Sweet Taste. The mechanism of sweetness perception has been extensively studied because of its commercial importance. Many substances that vary in chemical structure have been discovered which are similar to the taste of sucrose. Commercial sweeteners include sucralose, acesulfame-K, saccharin, aspartame, cyclamate (Canada) and the protein thaumatin 4), Each sweetener is unique in its perceived sensation because of the time to the onset of sweetness and to maximum sweetness, ability to mask other sensations, persistence, aftertaste and intensity relative to sucrose [TABLE IT. For example, the saccharides, sorbitol and... 

From the experimental results, it could be concluded that sweetness and bitterness are recognized in the same taste receptor and the receptor discriminates between bitter and sweet tastes based upon the difference in the functional unit combination. The currently accepted theory is that sweemess and bitterness are recognized by individual specific taste receptors. Data from this laboratory propose an alternative mechanism. Data is presented low to demonstrate which theory is most plausible. 

The current accepted theory suggests that a bitter compound and a sweet compound bind independently at specitic receptors. This situation will be referred to as "independent" in this report. The data to follow will demonstrate that a bitter compound and a sweet compound bind at the same receptor in a competitive manner. Therefore, this situation will be referred to as "competitive" in this report. Which theory was the functioning mechanism of taste reception should be determinable when one measured the taste intensities of mixed solutions of bitter and sweet tasting compounds. In this experiment the mechanism could be predicted to elicit a considerable difference in taste intensity and response that was varying based on the final concentration of each component. The "independent" receptor mechanism would be expected to yield data in which the intensities of bitter and sweet would be unaffected by mixing the two tastes, no matter what the concentration. On the other hand, with the "competitive" receptor mechanism one would expect both flavors to become altered, i.e., one stronger and the other weaker, as component concentrations varied the latter would occur because of competition of the substances for the same site. 

Nagarajan, S. Kellogg, M. S. DuBois, G. E. Williams, D. S. Gresk, C. J. Markos, C. S. Understanding the Mechanism of Sweet Taste Synthesis of Tritium Labeled Guanidineacetic Acid, J. Labelled Compounds and Radio-pharmaceut. 1992, 31, 599-607. 

T. Suami, L. Hough, M. Tsuboi, T. Machinami, and N. Watanabe, Molecular mechanisms of sweet taste. V. Sucralose and its derivatives, J. Carbohydr. Chem. 73 1079 (1994). 

One problem that remains is the mode of interaction between the sweet peptides and the receptor site. Despite a great number of studies, the mechanism of action of sweet stimuli on the receptor is not well known. Stereoisomerism can be responsible for differences in taste responses, and space-filling properties are also very important. These facts suggest that the receptor site exists in a three-dimensional structure. In this connection, the sense of sweet taste is subject to the "lock and key" of biological activity. 

Human taste response is modified by several plant-derived substances. The detergent sodium dodecyl sulfate, as well as triterpene saponins from the leaves of several plant species (most notably Gymnema sylvestre and Ziziphus jujuba) will temporarily inhibit the sweet taste sensation in man the duration of the effect being about one hour for G. sylvestre and about fifteen minutes for Z. jujuba. The mechanism of action seems to be related, in part, to the surfactant properties of the materials. Structures of the modifiers and possible mechanisms of action are discussed. 

Hashiguchi Y, Nishida M (2007) Evolution of trace amine associated receptor (TAAR) gene family in vertebrates lineage-specific expansions and degradations of a second class of vertebrate chemosensory receptors expressed in the olfactory epithelium. Mol Biol Evol 24 2099-2107 Hashiguchi Y, Furuta Y, Kawahara R, Nishida M (2007) Diversification and adaptive evolution of putative sweet taste receptors in threespine stickleback. Gene 396 170-179 Hemess MS, Gilbertson TA (1999) Cellular mechanisms of taste transduction. Annu Rev Physiol 61 873-900... 

Do these diverse compounds give rise to a common perception of sweetness or to qualitatively different sensations Sweetness does indeed appear to be a unitary percept (Breslin et al. 1994,1996). However, some sweeteners may be discriminable on the basis of their activation of other sensory transduction mechanisms or differences in the temporal properties of their sensory action. For example, the sweetener sodium saccharin activates bitter receptors in some people (Kuhn et al. 2004 Pronin et al. 2007), and also inhibits sweet taste at high concentrations (Galindo-Cuspinera et al. 2006). Sweet proteins such as thaumatin and monellin can have a slow onset or evoke a prolonged sweetness compared with sugars (Faus 2000), likely owing to a relatively high affinity for the sweet taste receptor. 

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