Fly sniffs molecule's quantum vibrations

http://www.newscientist.com/article/dn20130-fly-sniffs-molecules-quantum-vibrations.html

Fly sniffs molecule's quantum vibrations
* 20:00 14 February 2011 by Rachel Courtland

How does a nose generate the signals that the brain registers as smell? The conventional theory says it's down to the different shapes of smelly molecules. But fruit flies have now distinguished between two molecules with identical shapes, providing the first experimental evidence to support a controversial theory that the sense of smell can operate by detecting molecular vibrations.

The noses of mammals, and the antennae of flies, are lined with different folded proteins that form pocket-shaped "receptors". It has been generally assumed that a smell arises when an odour molecule slides into a receptor like a key in a lock, altering the receptor's shape and triggering a cascade of chemical events that eventually reach the brain. But this "shape" theory has limitations. For one, it can't easily explain why different molecules can have very similar smells.

In 1996, Luca Turin, a biophysicist now at the Massachusetts Institute of Technology, proposed a solution. He revived a theory that the way a molecule vibrates can dictate it odour, and came up with a mechanism to explain how this might work.

His idea was that electrons might only be able to pass across a receptor if it was bound to a molecule that vibrated at just the right frequency. Ordinarily, the energy needed for the electron to make this journey would be too great, but the right vibrational energy could prompt a quantum effect in which the electron "tunnels" through this energy barrier, and this would then be detected and registered as a particular smell (see diagram).

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Experiments are planned in another type of mammal. Several years ago John Sagebiel of the University of Nevada, Reno and Mary Cablk of the Desert Research Institute in Reno, Nevada, found that their pet dog, an Australian shepherd, seemed to be able to tell apart ordinary acetophenone and a deuterated version. They are now applying for funding to see if these informal results hold up in other dogs.

Journal reference: Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1012293108