Snapshot Issue 16 November 2005

Adenosine deaminase

There are those who sleep well. And those who don’t. Besides disorders which can result from ‘going through a bad time’ or ‘too much coffee’ for instance, could the quality of our sleep possibly be heritable? Yes, suggest Hans-Peter Landolt and his team of researchers from the University of Zürich.

It has been suspected for decades now that adenosine – a neuromodulator – has something to do with our sleep. Not surprisingly perhaps, it was later discovered that caffeine – whose effects on wakefulness are now common knowledge – acts as an adenosine antagonist and can bind to the neuromodulator’s receptor. This news gave no insight as to how adenosine affected sleep in detail but showed that it certainly could.

Adenosine accumulates in the brain during the day, as the remnants of energy molecules such as ATP. An enzyme – adenosine deaminase – then breaks it down overnight. Adenosine deaminase, or ADA, has a number of variants, many of which are at the heart of serious immune diseases. But one variant in particular, which is found in about 10% of the population, was shown to have a direct consequence in the quality and the length of that lovely deep sleep we all seek. The one most of us glide into during the first half of the night and which can last to varying degrees.

What was observed is that this specific ADA variant breaks down adenosine at a slower rate than the more common ADA. As a consequence, adenosine hangs around the brain of deep sleepers a little longer. Other than that, what is going on the molecular level is unknown. However, the knowledge that ADA can be found not only in the cytosol where it breaks down adenosine but also on a cell’s membrane where it has been shown to bind to adenosine receptors…and on which caffeine has an effect…is interesting.

Sleep, though, is the strangest of substances. Like our mood, it is subject to shifts which are dependent on so many environmental, emotional, physiological – to name but a few – factors. Blaming only ADA for the quality of our sleep – be it deep or not – would be narrow-minded. The good part is that a greater knowledge of ADA could open prospects for novel therapies in the battle against sleep disorders such as insomnia. Although scientists have no way of saying whether the quality and the length of deep sleep is indeed beneficial to us or not…

Also read: Protein Spotlight Issue no 8.

Adenosine deaminase, Homo sapiens (Human): P00813

L'édition française de cette chronique est disponible dans l'Instantanés du mois de Prolune.

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