Studies of electron transport dynamics in photosynthetic reaction centers using fast temperature changes

Rates of thermoinduced conformational transitions of reaction center (RC) c omplexes providing effective electron transport were studied in chromatopho res and isolated RC preparations of various photosynthesizing purple bacter ia using methods of fast freezing and laser-induced temperature jump. React ions of electron transfer from the primary to secondary quinone accepters a nd from the multiheme cytochrome c subunit to photoactive bacteriochlorophy ll dimer were used as probes of electron transport efficiency. The thermoin duced transition of the acceptor complex to the conformational state facili tating electron transfer to the secondary quinone acceptor was studied, it was shown that neither the characteristic time of the thermoinduced transit ion within the temperature range 233-253 K nor the characteristic time of s pontaneous decay of this state at 253 K exceeded several tens of millisecon ds. In contrast to the quinone complex, the thermoinduced transition of the macromolecular RC complex to the state providing effective electron transp ort from the multiheme cytochrome c to the photoactive bacteriochlorophyll dimer within the temperature range 220-280 K accounts for tens of seconds. This transition is thought to be mediated by large-scale conformational dyn amics of the macromolecular RC complex.