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Using a molecular approach to understanding human taste perception, researchers have made a new finding demonstrating that each individual's personal set of taste-receptor alleles, or gene variations, codes for distinct receptor proteins that determine individual differences in bitter-taste perception. These differences in perception are ubiquitous, underscoring the idea that, owing to slight variations in our genes for taste receptors, we all live in our own "taste worlds." Thus, we all perceive everyday foods such as teas, coffees, vegetables, meats, beer, cheeses, wines, and chocolates in our own way, potentially with no two tasters exactly alike.
The reasons for these perceptual differences involve myriad genes and environmental influences, as well as the interplay between these two factors. The new finding regarding bitterness perception suggests that the taste-receptor genes and their multiple alleles play a dominant role in determining how we perceive the world of tastes.
The longest-recognized and most famous genetically determined taste difference among people is the ability to taste PTC (phenylthiocarbamide) as bitter. PTC taste sensitivity varies tremendously among people; the threshold amount of PTC perceptible by individuals varies over a 1000-fold difference in concentration. These different sensitivities form a bimodal distribution in almost every population examined, and this distribution was interpreted as evidence that simple genetic differences, possibly involving only a single gene, underlie the PTC perceptual phenotype. The result was an 80-year-old search for the gene, which was identified last year.
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In the new work, four teams of researchers, including Paul Breslin, Danielle Reed, and Christopher Tharp from the Monell Chemical Senses Center, Dennis Drayna and Un-Kyung Kim from the NIH, Bernd Bufe, Christina Kuhn, and Wolfgang Meyerhof from the German Institute of Human Nutrition (DiFE), and Jay Slack from the Givaudan Corporation, demonstrate that an individual's taste sensitivity to PTC and a related compound, PROP, agrees very closely with the sensitivity of their specific PTC taste receptor. To test how sensitive different versions of the receptor were to the compounds, the researchers introduced different alleles of the gene into cultured cells, which then expressed the corresponding taste receptor protein.
A specialized assay allowed the researchers to determine the sensitivity of the protein receptor to bitter compounds at the cellular level, free of complicating factors such as the action of other taste receptors and the influence of individual taste experience.
The researchers found evidence that each person's specific allele of a single bitter-taste-receptor gene determines his or her perceptual sensitivity--determined by psychophysical tests--surprisingly well. In addition, tests on three sample populations also demonstrated that perception of higher concentrations of these bitter compounds is largely determined by which alleles an individual possesses. Thus, the ubiquitous taste differences that make us perceptually distinct are explained to a large degree by which form of the genes that code for our taste receptor proteins each of us carries.
Bernd Bufe, Paul A. S. Breslin, Christina Kuhn, Danielle R. Reed, Christopher D. Tharp, Jay P. Slack, Un-Kyung Kim, Dennis Drayna, and Wolfgang Meyerhof: "The Molecular Basis of Individual Differences in Phenylthiocarbamide and Propylthiouracil Bitterness Perception"
Publishing in Current Biology, Volume 15, Number 4, February 22, 2005. www.current-biology.com
Journal
Current Biology