Scientists Find New Taste Receptor
WASHINGTON (Reuters) - January 24, 2000 - Researchers said on Monday
they had identified the molecule in the tongue that helps people taste
umami, the ``fifth taste'' also known as monosodium glutamate (MSG) that
gives many Asian foods their punch.
The four major tastes in food are usually identified as sweet, salty,
sour and bitter, but many experts have argued that the umami taste is
not only unique but is equally important.
Nirupa Chaudhari and colleagues at the University of Miami School of
Medicine knew that the body is extremely sensitive to glutamate, which
is found in many protein-containing foods, including meat, seafood and
aged cheese.
Glutamate is also used as a neurotransmitter, or message-carrying
chemical, in the brain. Neurons have a variety of receptors designed to
detect its presence.
Such receptors, which are a kind of chemical doorway, should
theoretically be used by cells on the tongue to detect glutamate in
food. In fact, one of them, a protein called mGluR4, is found in taste
buds.
But mGluR4 is so sensitive to glutamate that if any umami taste is
present in a food at all, it should overwhelm all other tastes. Also,
molecules that block the protein do not block the ability to taste
umami.
Writing in the journal Nature Neuroscience, Chaudhari and colleagues
said they had figured out why this does not happen.
Using taste buds from young rats, which seem to taste glutamate in the
same way people do, they found a truncated version of mGluR4. This
chopped-off form of the protein can detect umami, but is not as
sensitive to it as brain cells are.
``The similarity of its properties to MSG taste suggests that this
receptor is a taste receptor for glutamate,'' they wrote in their
report.
Umami was first identified as a distinct taste in 1908 by Kikunae Ikeda
of the Tokyo Imperial University, who was struck by the distinctive
flavor of seaweed broth. He isolated and identified the glutamate
molecule.
Copyright © 2000 Reuters Limited.
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Judith Richards, London, Ontario, Canada
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