The Taste of Carbonation

Gee Fizz The next time you enjoy a carbonated beverage, you can do so with an enhanced understanding of the molecular mechanism that provides its distinctive flavor sensation. Chandrashekar et al. (p. 443 ) genetically ablated specific sets of taste cells in mice and found that the sensation of CO 2 was lost in animals lacking taste cells that sense sour flavors. A screen for genes specifically expressed in these cells revealed the gene encoding carbonic anhydrase 4, which catalyzes hydration of CO 2 to form bicarbonate and free protons. Knockout animals not expressing the carbonic anhydrase 4 gene also showed diminished sensation of CO 2 . The protons produced by the enzyme appear to be the actual molecules sensed by the sour-sensitive cells. This process, combined with tactile sensations, appears to be the source of the popular fizzy sensation.