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Biological Chemistry

Sour Cells Sense Carbonation

Carbonic anhydrase on our taste buds' sour-sensing cells produce the fizzy taste of carbonated drinks

by Jyllian N. Kemsley
October 19, 2009 | A version of this story appeared in Volume 87, Issue 42

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Credit: Science
Sites of carbonic anhydrase production (red) overlap with sour sensing cells (green) in mouse taste buds (areas that overlap are yellow.
Credit: Science
Sites of carbonic anhydrase production (red) overlap with sour sensing cells (green) in mouse taste buds (areas that overlap are yellow.

An enzyme on the surface of sour-sensing cells is the key to tasting the carbonation in your favorite fizzy drink, reports a group led by Charles S. Zuker of Columbia University (Science 2009, 326, 443). Mammals have multiple sensory systems that respond to the CO2, but the molecular mechanisms of those systems are poorly understood. Zuker and colleagues blocked the function of selective classes of taste receptor cells to try to pin down the mechanism for tasting CO2. They found that sour-sensing cells are also the ones that respond to CO2. The group then used gene-expression profiling to narrow in on an extracellular carbonic anhydrase as the essential enzyme. Carbonic anhydrase converts CO2 to HCO3 and H+. Further investigation revealed that it is likely the H+ in particular that signals CO2 reception to taste cells. The authors suggest that the carbonic anhydrase may principally work to maintain the pH balance within taste buds, and its function as a carbonation detector may be merely “an accidental consequence.”

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