Fruit flies can detect heavy hydrogen: study

Feb 16, 2011 by Lin Edwards report
In the present study wildtypes of different origin were shown to be quite different in their behavior towards odors of different origin. Credit: Rickard Ignell

(PhysOrg.com) -- A new study by researchers in Greece and the US has found that fruit flies can discriminate between normal and heavy hydrogen (deuterium) isotopes, which adds weight to a new theory of how the sense of smell works.

Dr Efthimios Skoulakis of the Alexander Fleming Biomedical Sciences Research Center in Vari, Greece and colleagues presented (Drosophila melanogaster) with acetophenone, an odorant molecule often used in perfumes, in a T-shaped maze. In one branch the molecule contained normal hydrogen, while in the other the in the molecule were replaced by deuterium. The flies were able to choose the branch they preferred.

The fruit flies, which are known to have a strong sense of smell, showed a definite preference for the molecule with more hydrogen and their aversion to the deuterated molecule grew as more hydrogens were replaced. When fruit flies that had been genetically modified to have no were used, they showed no preference.

The fruit flies’ ability to discriminate between the molecules was also demonstrated by successfully giving the flies mild electric shocks to their feet as they walked on the floor of the maze to condition them to selectively avoid either form of the molecule.

Dr Skoulakis said the results support a new theory of olfaction first proposed in 1996 by co-author Dr Luca Turin, a biophysicist who is now at the Massachusetts Institute of Technology in Cambridge in the US. The new theory suggests odorants are detected by their vibrations rather than by their shape.

Deuterium differs from the normal isotope of hydrogen in that its nucleus contains a proton and a neutron instead of just a proton. This roughly doubles the mass of the deuterium atom, and so while it has similar properties to normal hydrogen, the larger mass means bonds between and other atoms within molecules vibrate more slowly.

The leading theory of how smell works is that odorant are detected by receptor proteins in the olfactory membranes because of their shape, which fits into the shape of a cavity in the protein, like a key in a lock. If the molecule fits a signal is sent to the brain.

Dr Turin’s theory is that the electrons of the odorant might be able to cross a receptor membrane only if the bonds in the molecule are vibrating at exactly the right frequency. Since an odorant with normal hydrogen will have different vibrational properties to the deuterated odorant, the two odorants should smell different even though their shape is the same.

As further confirmation the researchers tested the fruit flies with nitriles, which have a similar vibrational frequencies to that of deuterium-carbon bonds. The fruit flies had an aversion to the nitriles as expected.

Humans have not been shown to have the ability to discriminate between compounds containing normal and heavy , but Dr Turin said there were unpublished reports of a similar ability in at least one dog, which ignores an odorant it is trained to detect if the molecule is deuterated.

The paper is published in the journal Proceedings of the National Academy of Sciences (PNAS).

Explore further: Engineers devise technology for rapidly testing drug-delivery vehicles in zebrafish

More information: Molecular vibration-sensing component in Drosophila melanogaster olfaction, PNAS, Published online before print February 14, 2011, doi:10.1073/pnas.1012293108

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antialias
2.3 / 5 (3) Feb 16, 2011
Interesting. It was always thought that the chemical properties of molecules are identical if you replace an atom with one of its isotopes. Now it seems that the chemical properties do vary ever so slightly (or at least that the bridge from chemical receptor to chemoelectric neural pathways vary) with the isotope.

Small though this may sound: this could open up new ways of understanding and tayloring enzymes/antigens and other key-lock chemical systems. Now we not only can look at the shape but also at the electron densities (or even vibration modes) to understand why a particular protein works or doesn't work.
Parmanello
3.7 / 5 (3) Feb 16, 2011
It wasn't always thought that - it's well known heavy water is dangerous as it interferes with sensitive biochemical reactions.
jjoensuu
4 / 5 (3) Feb 16, 2011
it's well known heavy water is dangerous as it interferes with sensitive biochemical reactions.


So I was wondering what was the benefit of that code between fruit flies ears that tells it that substances with deuterium atoms are less desirable. But looks like you answered that, thanks!
antialias
5 / 5 (3) Feb 16, 2011
Since deuterium is not very abundant in nature (about 1 in 6000 hydrogen atoms is deuterium) I doubt that detecting deuterium as not desirable is a relevant selection factor in the evolutionary process of fruit flies.

There is no real benefit. But the electrochemical properties of deuterium seem just different enough to make the receptor behave differently.
Johannes414
1 / 5 (9) Feb 16, 2011
God said: let there be light, and there was light. God said: fruitfly, and there was a fruitfly with all functions intact. No evolution required.
A_Paradox
not rated yet Feb 16, 2011
well my first thought was to wonder whether the plan was to train an army [swarm?] of fruit flies to sort through a billion tonnes of fresh water to help with supplies of moderator water for nuclear reactors.

:-)
A_Paradox
not rated yet Feb 16, 2011
well my first thought was to wonder whether the plan was to train an army [swarm?] of fruit flies to sort through a billion tonnes of fresh water to help with supplies of moderator water for nuclear reactors.
A_Paradox
not rated yet Feb 16, 2011
oops, the page didn't react like physorg usually does; some message about xml didn't know what it was doing.
gwrede
1 / 5 (1) Feb 16, 2011
oops, the page didn't react like physorg usually does; some message about xml didn't know what it was doing.
Your message almost always has gone through. You can check this by going to the main page and clicking the link of the same page again.
It was always thought that the chemical properties of molecules are identical if you replace an atom with one of its isotopes.
The chemical proerties are. But the physical properties are just a bit different.
Going
1 / 5 (1) Feb 16, 2011
I never really believed that smell is based on the body having a vast array of shape receptors each wired into the brain with its own smell sensation. A small step, I hope , towards the Vibration theory of Olfaction which makes more sense.
Telekinetic
1 / 5 (3) Feb 16, 2011
It wasn't always thought that - it's well known heavy water is dangerous as it interferes with sensitive biochemical reactions.


Actually, I take a product, and this is not a plug, called Cellfood, which is a deuterium-based nutrient that has an interesting development history. An M.D.
whose opinion I trust recommended it.
antialias
not rated yet Feb 17, 2011
The chemical proerties are. But the physical properties are just a bit different.

Actually that's the weird thing. With the low mass of hydrogen the chemical properties actually do differ between hydrogen and deuterium. The heavier the element the less pronounced this effect becomes between the element and its isotopes.

From wikipedia (deuterium):
... its large mass difference with protium (1
H) (deuterium has a mass of 2.014102 u, compared to the mean hydrogen atomic weight of 1.007947 u, and protium's mass of 1.007825 u) confers non-negligible chemical dissimilarities with protium-containing compounds...


It's simply amazing that this small effect would still make a difference in the reaction of a large molecule with some deuterium instead of protium (regular hydrogen)
physpuppy
not rated yet Feb 17, 2011
What happens in many reactions, and more often in biochemical reactions you have competing processes taking place. If the Hydrogen exchange is the limiting step of the reaction (or changes the limiting step of reaction) by replacing Hydrogen with Deuterium, the reaction can have a different outcome. You're changing the kinetics of the reaction.
smellyfly
not rated yet Apr 07, 2011
The odorant receptors in flies are very different than the odorant receptors in humans. So even if a fly uses vibrational modes of odorants to activate odorant receptors, this by no means the same occurs in humans. In fact, there is good evidence that this does not happen in humans (Keller and Vosshall Nat Neuro 2004). I've read this recent PNAS paper and a number of experiments still remain to be done to really support his model even for fly olfaction. For example, he should look at the antennal lobe of the fly and measure the activity of the olfactory receptor neurons. Presumably, the heavy odorants should be activating novel classes of odorant receptors which should be visible. In addition, T-maze experiments can be prone to experimental error.