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Rogue odour theory could be right

Publication date: Dec 12, 2006 3:14:01 PM

A controversial theory that explains the molecular mechanism which gives our sense of smell razor-sharp precision has been given a boost thanks to a study by a team of UCL researchers at the London Centre for Nanotechnology (LCN).

Reporting in an upcoming edition of the journal Physical Review Letters, they demonstrate that vibration theory, the process by which the body distinguishes one odour molecule from another by the way it vibrates, is viable.

Like many other biological processes, it was previously thought that on a molecular level our sense of smell was governed by shape recognition: the way a particular molecule binds to a complementary receptor – acting in a mechanism similar to a lock and key.

But this theory struggles to explain why very different shaped molecules can smell similar or why some molecules of essentially the same shape but made of heavier versions of the atoms have a very different smell.

Dr Andrew Horsfield, of the London Centre for Nanotechnology, the UCL Department of Physics & Astronomy and one of the senior authors of the study, says: “Vibration theory has been around for a while but has lacked the answer to a crucial question: how could a biological system make the kind of measurements of vibrations which normally require a piece of lab kit like a spectroscope. This mechanism is more like swipe-card identification than a key fitting a lock.

“Back in 1996, a UCL researcher, Dr Luca Turin* revived the theory by suggesting that smell receptors acted like switches tuned to different frequencies across the vibration spectrum. When an odorant molecule with the correct vibration binds to the receptor it closes the switch and allows the electrons to flow. This signal is amplified and sent to the brain. Each molecule has a distinctive vibration pattern and therefore a unique smell. However, Turin’s proposal lacked mathematical rigour and the physical mechanism to back it up.”

In the latest UCL paper, the researchers propose a viable physical mechanism that fits with both the laws of physics and observed features of smell.

Professor Marshall Stoneham, of the London Centre for Nanotechnology, the UCL Department of Physics & Astronomy and one of the senior authors of the study, added: “The key to determining whether the vibration model works lies in the rate that electrons move around either in the presence or absence of an odour. Our calculations show that electron flow increases significantly in the presence of an odour, suggesting there’s mileage in vibration theory.

“Furthermore, this type of receptor activation, which essentially relies on ‘biological electronics’, was previously unknown and could explain how other systems in the body operate.”

-end-

Notes for Editors

* Dr Luca Turin is now employed by the odorant design company, Flexitral.

1. For more information, please contact:

Dr Andrew Horsfield, London Centre for Nanotechnology, Email: a.horsfield@ucl.ac.uk, Phone: +44 (0)20 7679 7701

Judith H Moore, UCL Media Relations Manager, Tel: +44 (0) 20 7679 7678, Mobile: +44 (0)77333 075 96, Out-of-hours: +44 (0)7917 271 364, Email: judith.moore@ucl.ac.uk

2. ‘Could humans recognize odor by phonon assisted tunnelling’ is published in the journal Physical Review Letters in December. The authors are Professor Marshall Stoneham, Dr Andrew Horsfield and graduate students Jennifer Brookes.