The Molecular Mechanism of Thermal Noise in Rod Photoreceptors
- 7 September 2012
- journal article
- other
- Published by American Association for the Advancement of Science (AAAS) in Science
- Vol. 337 (6099), 1225-1228
- https://doi.org/10.1126/science.1220461
Abstract
Spontaneous electrical signals in the retina's photoreceptors impose a limit on visual sensitivity. Their origin is attributed to a thermal, rather than photochemical, activation of the transduction cascade. Although the mechanism of such a process is under debate, the observation of a relationship between the maximum absorption wavelength (λmax) and the thermal activation kinetic constant (k) of different visual pigments (the Barlow correlation) indicates that the thermal and photochemical activations are related. Here we show that a quantum chemical model of the bovine rod pigment provides a molecular-level understanding of the Barlow correlation. The transition state mediating thermal activation has the same electronic structure as the photoreceptor excited state, thus creating a direct link between λmax and k. Such a link appears to be the manifestation of intrinsic chromophore features associated with the existence of a conical intersection between its ground and excited states.Keywords
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