Temperature dependence of protein fluorescence in Rb. sphaeroides reaction centers frozen to 80 K in the dark or on the actinic light as the indicator of protein conformational dynamics

The differences in the average fluorescence lifetime (τ av ) of tryptophanyls in photosynthetic reaction center (RC) of the purple bacteria Rb. sphaeroides frozen to 80 K in the dark or on the actinic light was found. This difference disappeared during subsequent heating at the temperatures above 250 K. The computer-based calculation of vibration spectra of the tryptophan molecule was performed. As a result, the normal vibrational modes associated with deformational vibrations of the aromatic ring of the tryptophan molecule were found. These deformational vibrations may be active during the nonradiative transition of the molecule from the excited to the ground state. We assume that the differences in τ av may be associated with the change in the activity of these vibration modes due to local variations in the microenvironment of tryptophanyls during the light activation.