Thermal deactivation of excitation in bacterial reaction centres embedded in gel

Bacterial photosynthetic reaction centres from Rhodobacter sphaeroides stra in (R-26) were immobilized in polyacrylamide gel. The samples of RC in gel were incubated with reducing-oxidizing agents in order to reach four variou s redox potentials of samples and then they were dried in vacuum to fix the obtained redox states of chromophores of reaction centres. For such sample s the absorption and photoacoustic spectra were measured with and without a dditional illumination. The illumination caused the changes in absorption a nd in photoacoustic spectra. The changes depend on redox potential of the s ample and spectral region. The yield of thermal deactivation for various ba cteriochlorophyll and bacteriopheophitin bands was different what suggests that the contributions to various bands from the pigment forms characterize d by different yield of photochemical reaction are different. The electron transfer process caused by illumination and thermal dissipation-of excitati on are mutually competitive processes. The chromophores engaged in electron transfer are less effective in thermal deactivation of excitation. Electro n back transfer from quinone to photo oxidized special pair of reaction cen tre embedded in gel occurs in about 0.1 s, for all investigated redox state s. (C) 1999 Elsevier Science S.A. All rights reserved.