Phenylthiocarbamide

Phenylthiocarbamide (PTC), also known as phenylthiourea (PTU), is an organosulfur thiourea containing a phenyl ring.

Phenylthiocarbamide
Names
Preferred IUPAC name
Phenylthiourea
Other names
N-Phenylthiourea
1-Phenylthiourea
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.002.865
MeSH Phenylthiourea
UNII
Properties
C7H8N2S
Molar mass 152.22 g·mol−1
Appearance White to slightly yellow powder
Density 1.294 g/cm3
Melting point 145 to 150 °C (293 to 302 °F; 418 to 423 K)
Soluble in boiling water
Hazards
T+
NFPA 704 (fire diamond)
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilHealth code 4: Very short exposure could cause death or major residual injury. E.g. VX gasReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
1
4
0
Lethal dose or concentration (LD, LC):
3 mg/kg (oral, rat)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

It has the unusual property that it either tastes very bitter or is virtually tasteless, depending on the genetic makeup of the taster. The ability to taste PTC is often treated as a dominant genetic trait, although inheritance and expression of this trait are somewhat more complex.[1][2]

PTC also inhibits melanogenesis and is used to grow transparent fish.[3]

About 70% of people can taste PTC, varying from a low of 58% for Indigenous Australians and indigenous peoples of New Guinea to 98% for indigenous peoples of the Americas.[4] One study has found that non-smokers and those not habituated to coffee or tea have a statistically higher percentage of tasting PTC than the general population.[5][6] PTC does not occur in food, but related chemicals do, and food choice is related to a person's ability to taste PTC.[5][7]

History

The tested genetic taste phenomenon of PTC was discovered in 1931 when DuPont chemist Arthur Fox accidentally released a cloud of fine crystalline PTC. A nearby colleague complained about the bitter taste, while Fox, who was closer and should have received a strong dose, tasted nothing. Fox then continued to test the taste buds of assorted family and friends, setting the groundwork for future genetic studies. The genetic penetrance was so strong that it was used in paternity tests before the advent of DNA matching.[8]

The PTC taste test has been widely used in school and college practical teaching as an example of Mendelian polymorphism in human populations. Based on a taste test, usually of a piece of paper soaked in PTC (or the less toxic propylthiouracil (PROP)), students are divided into taster and non-taster groups. By assuming that PTC tasting is determined by a dominant allele at a single autosomal gene, and that the class is an unbiased sample from a population in Hardy–Weinberg equilibrium, students then estimate allele and genotype frequencies within the larger population. While this interpretation is broadly consistent with numerous studies of this trait, it is worth noting that other genes, sex, age and environmental factors influence sensitivity to PTC.[1][2] Also, there are several alleles segregating at the major gene determining the taste of PTC, particularly in African populations, and the common "taster" allele is incompletely dominant (homozygotes for this allele are more sensitive to PTC than are heterozygotes).[2][9] Additionally, PTC is toxic and sensitivity to the substitute, PROP, does not show a strong association with the gene controlling ability to taste PTC.[2]

Role in taste

There is a large body of evidence linking the ability to taste thiourea compounds and dietary habits. Much of this work has focused on 6-propyl-2-thiouracil (PROP), a compound related to PTC that has lower toxicity.[4] A supertaster has more of an ability to taste PTC. On the other hand, heavy cigarette smokers are more likely to have high PTC and PROP thresholds (i.e. are relatively insensitive).

In 1976, an inverse relationship between taster status for PTC and for a bitter component of the fruit of the tree Antidesma bunius was discovered.[10] Research on the implications still continues.

Ability to taste PTC may be correlated with a dislike of plants in the genus Brassica, presumably due to chemical similarities. However, studies in Africa show a poor correlation between PTC tasting and dietary differences.[9]

Genetics
Main article: PTC tasting

Much of the variation in tasting of PTC is associated with polymorphism at the TAS2R38 taste receptor gene.[11] In humans, there are three SNPs (single nucleotide polymorphisms) along the gene that may render its proteins unresponsive.[12] There is conflicting evidence as to whether the inheritance of this trait is dominant or incompletely dominant.[2] Any person with a single functional copy of this gene can make the protein and is sensitive to PTC. Some studies have shown that homozygous tasters experience a more intense bitterness than people that are heterozygous; other studies have indicated that another gene may determine taste sensitivity.[1]

The frequency of PTC taster and non-taster alleles vary in different human populations.[13] The widespread occurrence of non-taster alleles at intermediate frequencies, much more common than recessive alleles conferring genetic disease, across many isolated populations, suggests that this polymorphism may have been maintained through balancing selection.[9]

Chimpanzees and orangutans also vary in their ability to taste PTC, with the proportions of tasters and non-tasters similar to that in humans.[14] The ability to taste PTC is an ancestral trait of hominids that has been independently lost in humans and chimpanzees, through distinct mutations at TAS2R38.[15]

Non-taster phenotype distribution (%) in selected populations
Results of multiple PTC taste tests in different regions done with the discrimination method developed by Harris and Kalmus in 1949, published in Annals of Eugenics.[16]
Location# of ParticipantsNon-taster %References
Bosnia and Herzegovina 7,362 32.02 Hadžiselimović et al. (1982)[17]
Croatia 200 27.5 Grünwald, Pfeifer (1962)
Czech Republic 785 32.7 Kubičkova, Dvořaková (1968)
Denmark 251 32.7 Harrison et al. (1977)[18]
England 441 31.5 Harrison et al. (1977)[18]
Hungary 436 32.2 Forai, Bankovi (1967)
Italy 1,031 29.19 Floris et al. (1976)
Montenegro 256 28.20 Hadžiselimović et al. (1982)[17]
Užice, Serbia 1,129 16.65 Hadžiselimović et al. (1982)[17]
Voivodina, Serbia 600 26.3 Božić, Gavrilović (1973)
Russia 486 36.6 Boyd (1950)
Slovenia 126 37.3 Brodar (1970)
Spain 204 25.6 Harrison et al. (1977)[18]

See also

References
  1. Guo; Reed, D. R. (2001). "The genetics of phenylthiocarbamide perception". Annals of Human Biology. 28 (2): 111–142. doi:10.1080/03014460151056310. PMC 3349222. PMID 11293722.
  2. McDonald, John H. "PTC tasting: The Myth". Myths of Human Genetics. Retrieved 11 May 2015.
  3. Karlsson, Johnny; von Hofsten, Jonas; Olsson, Per-Erik (2001). "Generating Transparent Zebrafish: A Refined Method to Improve Detection of Gene Expression During Embryonic Development". Marine Biotechnology. 3 (6): 522–527. doi:10.1007/s1012601-0053-4. PMID 14961324. S2CID 7980753.
  4. Kim U, Wooding S, Ricci D, Jorde LB, Drayna D (2005). "Worldwide haplotype diversity and coding sequence variation at human bitter taste receptor loci". Human Mutation. 26 (3): 199–204. doi:10.1002/humu.20203. PMID 16086309.
  5. Fischer R, Griffin F, Kaplan AR (1963). "Taste thresholds, cigarette smoking, and food dislikes". Medicina Experimentalis. International Journal of Experimental Medicine. 9 (3): 151–67. doi:10.1159/000135346. PMID 14083335.
  6. Kaplan AR, Glanville EV, Fischer R (1964). "Taste thresholds for bitterness and cigarette smoking". Nature. 202 (4939): 1366. Bibcode:1964Natur.202.1366K. doi:10.1038/2021366a0. PMID 14210998. S2CID 4184237.
  7. Forrai G, Bánkövi G; Bánkövi (1984). "Taste perception for phenylthiourea and food choice—a Hungarian twin study". Acta Physiol Hung. 64 (1): 33–40. PMID 6541419.
  8. Lee Phillips M (15 July 2003). "Scientists Find Bitter Taste Gene". Retrieved 5 December 2009.
  9. Campbell; et al. (2012). "Evolution of Functionally Diverse Alleles Associated with PTC Bitter Taste Sensitivity in Africa". Molecular Biology and Evolution. 29 (4): 1141–1153. doi:10.1093/molbev/msr293. PMC 3341826. PMID 22130969.
  10. Henkin, R.I. & W.T. Gillis (1977). "Divergent taste responsiveness to fruit of the tree Antidesma bunius". Nature. 265 (5594): 536–537. Bibcode:1977Natur.265..536H. doi:10.1038/265536a0. PMID 834304. S2CID 1259447.
  11. Drayna, Dennis (2005). "Human Taste Genetics". Annual Review of Genomics and Human Genetics. 6: 217–235. doi:10.1146/annurev.genom.6.080604.162340. PMID 16124860.
  12. Kim UK, Jorgenson E, Coon H, Leppert M, Risch N, Drayna D (2003). "Positional cloning of the human quantitative trait locus underlying taste sensitivity to phenylthiocarbamide". Science. 299 (5610): 1221–1225. Bibcode:2003Sci...299.1221K. doi:10.1126/science.1080190. PMID 12595690. S2CID 30553230.
  13. Fareed, M.; Shah, A.; Hussain, R.; Afzal, M. (2012). "Genetic study of phenylthiocarbamide (PTC) taste perception among six human populations of Jammu and Kashmir (India)". Egypt J Med Hum Genet. 13 (2): 161–166. doi:10.1016/j.ejmhg.2012.01.003.
  14. Fisher, Ford & Huxley, R. A.; Ford, E. B.; Huxley, Julian (28 October 1939). "Taste-testing the Anthropoid Apes" (PDF). Nature. 144 (750): 750. Bibcode:1939Natur.144..750F. doi:10.1038/144750a0. hdl:2440/15129. S2CID 4136526.
  15. Wooding, Stephen; et al. (2006). "Independent evolution of bitter-taste sensitivity in humans and chimpanzees". Nature. 440 (7086): 930–934. Bibcode:2006Natur.440..930W. doi:10.1038/nature04655. PMID 16612383. S2CID 4395892.
  16. Harris, H.; Kalmus, H. (1949). "The measurement of taste sensitivity to phenylthiourea (PTC)". Ann. Eugen. 15 (1): 24–31. doi:10.1111/j.1469-1809.1949.tb02419.x. PMID 15403125.
  17. Hadžiselimović, R.; Novosel, V.; Bukvić, S.; Vrbić, N. (1982). "Distribucija praga nadražaja za ukus feniltiokarbamida (PTC) u tri uzorka stanovništva Jugoslavije". God. Biol. Inst. Univ. U Sarajevu. 35: 72–80.
  18. Harrison et al. (1977): Human biology – An introduction to human evolution, variation, growth and ecology. Oxford University Press, Oxford, ISBN 978-0-19-857164-3; ISBN 978-0-19-857165-0.
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