ИСТИНА

Phytochrome photoreceptor proteins regulate light adaptation of plants and bacteria by photoswitching between red-absorbing and far-red absorbing states. Using state of the art quantum chemistry calculations, we investigate how the chromophore-protein interactions define the photodynamics of the photoreceptor. The linear tetrapyrrole chromophore of phytochromes carries a positive charge. Despite the chromophore ionic nature, intra-chromophore charge transfer and electrostatic interactions do not play a crucial role in phytochrome color tuning. Instead, charge-transfer from the protein to the chromophore and chemical resonance are identified as essential molecular mechanisms.