Re: Human taste sensor for amino acids found

[Guest guest]

So, what biological reason is there that we have taste receptors for MSG?

>From: " Greg " <gowatson@...>

>Reply-

> " Health Optimal Health & Longevity "

><Optimal_Health_and_Longevity >

>Subject: [ ] Human taste sensor for amino acids found

>Date: Fri, 1 Mar 2002 14:41:15 +1030

>

>http://www.hhmi.org/news/zuker3.html

>

>Homing In On a Receptor for the Fifth Taste

>

> " Since amino acids are essential building blocks of biologically important

>molecules, it made evolutionary sense for

>there to be a taste pathway that would make amino acids attractive to

>consume, " said HHMI investigator Zuker.

>

>February 25, 2002— Humans can recognize five tastes: bitter, salty, sour,

>sweet and umami. Of the five, however, umami

>is the most difficult to describe — it’s the flavor associated with

>monosodium glutamate (MSG). Now, researchers have

>identified a taste receptor that responds to amino acids, including umami,

>and they hope to develop a more precise

>description of the molecular events that allow the brain to perceive the

>five different tastes.

>

>With the discovery of the new receptor, scientists have now identified

>taste receptors for amino acids, bitter and sweet

>tastes. Given that many amino acids are essential components of our diet,

>this work may also aid understanding of how

>animals, including humans, regulate nutritional intake to achieve a

>balanced diet. Better understanding of taste

>receptors may permit scientists in the food industry to formulate new

>products that have specific tastes.

>

>A research team led by Medical Institute investigator

>S. Zuker at the University of California,

>San Diego, and J. P. Ryba of the National Institutes of Health

>reported the identification of an amino-acid

>taste receptor in an advanced online publication in Nature on February 25,

>2002.

>

>Zuker’s and Ryba’s groups previously collaborated in discovering sweet and

>bitter taste receptors. After they had

>identified those receptors, they set their sights on finding a taste

>receptor for amino acids, reasoning that one must

>exist because it had long been known that humans have the ability to taste

>umami and other amino acids. " Since amino

>acids are essential building blocks of biologically important molecules

>such as proteins, it made evolutionary sense for

>there to be a taste pathway that would make amino acids attractive to

>consume, " said Zuker.

>

>In their search for the amino acid receptor, the scientists focused on T1R

>receptors, a family of proteins that are

>distantly related to receptors in the brain that recognize the amino acid

>glutamate and related chemicals. Different T1R

>genes can be expressed in cells in different combinations to yields cells

>that respond to a specific taste. For example,

>T1R2 and T1R3, designated T1R2+3, combine to function as a sweet receptor.

>

>To test various receptor possibilities, the scientists devised a human cell

>culture method in which combinations of T1R

>subunits were expressed in cells. This permitted the scientists to assess

>how cells bearing different combinations of

>T1R genes responded to particular amino acids.

>

>Using the cell culture technique, Greg , a graduate student in

>Zuker’s lab, discovered that the combination of

>cells bearing T1R1 and T1R3 functioned as a " broadly tuned " receptor that

>was stimulated by many amino acids. This

> " T1R1+3 " receptor combination was highly selective for L-amino acids, which

>are found in nature. D-amino acids, which

>are mirror images of L-amino acids and do not occur naturally, did not

>activate the receptor.

>

>The scientist also tested whether their newly identified amino acid

>receptor candidate behaved in a manner similar to

>receptors that recognize glutamate. A signature of the umami taste is that

>it is boosted by purine nucleotides, like

>IMP. In the cell cultures, IMP dramatically enhanced the response of T1R1+3

>to amino acids.

>

>The researchers next examined the effects of IMP in mice. They added the

>chemical to the animals’ taste buds, then added

>amino acids, and measured the specific response of nerve fibers connected

>to the taste buds that expressed T1R1+3. The

>response of these nerves was greatly enhanced by IMP.

>

>In a final set of experiments, and his colleagues showed that mice

>do not taste some artificial sweeteners such

>as aspartame and cyclamate that humans can taste because of sequence

>differences in the T1R receptors of the two

>species.

>

> " This last piece of the puzzle is worthy of note, " said Zuker. " Changes in

>the sequence of taste receptors appear to be

>responsible for some of the difference in tasting behavior between mice and

>humans. "

>

>According to Zuker, discovery of the amino acid taste receptor will have

>important implications for understanding the

>machinery of taste. " When Nick Ryba and I began this collaboration a bit

>over four years ago, our ultimate goal was to

>understand how the brain knows what you just tasted, " he said. " We wanted

>to discover how taste receptor cells are

>activated and how their signals travel to the brain to produce specific

>taste perceptions.

>

> " To do that, we first needed to define the different taste modalities at a

>cellular level, so that we could then follow

>their connectivity maps to the brain. The ‘Holy Grail’ in this field has

>been the receptors, and now that we know the

>receptors underlying three modalities – sweet, bitter and amino acid – we

>can begin to work on our original goal, to map

>this system to understand how taste is encoded, " Zuker said.

>========================

>Good health & long life,

> Greg ,

> http://optimalhealth.cia.com.au

>

>

>

>