Editors' ChoiceBiochemistry

Responding to Light and Heat

Science Signaling  11 Sep 2012:
Vol. 5, Issue 241, pp. ec242
DOI: 10.1126/scisignal.2003589

The protein rhodopsin is sensitive to dim light, but its sensitivity is limited by signals caused by the noise of thermal activation. The basis of this relationship, known as the Barlow correlation, has long been debated. A recent study suggested that thermal activation involves a canonical isomerization reaction. Gozem et al. confirm that isomerization is the rate-limiting step controlling thermal noise, and they provide a molecular understanding of the Barlow correlation. They use quantum mechanics coupled with molecular mechanics to show that the transition state mediating thermal activation has the same electronic structure as the photochemical excited state.

S. Gozem, I. Schapiro, N. Ferré, M. Olivucci, The molecular mechanism of thermal noise in rod photoreceptors. Science 337, 1225–1228 (2012). [Abstract] [Full Text]