Two teams of scientists have identified a protein on the surfaces of select tongue cells that may be the long-sought detector of sour taste.
People and some other animals, including mice, distinguish five recognized tastes: sweet, bitter, sour, salty, and umami, the flavor of monosodium glutamate. Over the past 6 years, researchers including Charles S. Zuker of the University of California, San Diego have ferreted out proteins on tongue-cell surfaces responsible for receiving sweet, bitter, and umami sensations.
To locate the sour-taste receptor, Zuker's team started with a few assumptions based on previous findings. For example, a sour-detecting protein would weave in and out of the membranes of tongue cells, as the taste receptors already identified do. Previous studies also suggested that each tongue cell produces no more than one type of taste receptor.
Zuker's team scanned the mouse genome, looking first for genes that encode membrane-spanning proteins that r