Quantum biology posits that non-trivial coherent macromolecular interactions can influence biological behavior. If and how nature can maintain coherence in a hot wet environment is unknown. Two-photon time-resolved fluorescence anisotropy, photon-antibunching, fluorescence correlation spectroscopy, and one-photon circular dichroism was used to demonstrate that homodimers of a yellow fluorescent protein (FP) behave coherently (excitonic coupling) at room temperature, and this coupling alters their ability to emit photons independently. This supports the hypothesis that FPs have evolved mechanisms to allow coherent interactions under physiological conditions. Since FPs are experimentally tractable, they are ideally suited for studying how nature can enable biological coherence.
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