It lasts just a trillionth of a second, one of the fastest processes in nature, but it is the fundamental chemical basis of vision, which occurs whenever light hits the retina: it has now been reconstructed for the first time in detail thanks to a powerful X-ray laser, from research coordinated by the Swiss Paul Scherrer Institute (PSI). The study, published in the journal Nature, literally sheds light on a molecular process that so far no one has been able to observe in real time, but which is the very first step in our ability to perceive light.
The protagonist of the scene is the human light receptor, rhodopsin: fixed to the center of this protein is a small molecule, retinal, which is a derivative of vitamin A. When light hits rhodopsin, the retinal absorbs part of the ‘energy and changes its three-dimensional shape in a fraction of a second, thus ‘turning on’ the switch of the eye and triggering the cascade of reactions which underlie the sense of sight. The point of departure and arrival of this mechanism has been known for some time, but the researchers led by Valérie Panneels and Gebhard Schertler have now also revealed what happens during the very rapid transition from one form to another of the protein.
The study authors found that, when rhodopsin absorbs light, it uses some of the energy to ‘inflate’ slightly, much like our chest does when we inhale air. During this sort of ‘respiration’, the protein momentarily loses contact with the retinal molecule inside it, thus leaving it free to rotate. Immediately afterwards the rhodopsin contracts again and ‘traps’ the retinal, only now it has to adapt to the new conformation: the process lasts only a picosecond, ie a trillionth of a second.
Source: Ansa
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