Green filamentous bacteria decay time

The RC of green filamentous bacteria contain a membrane-bound cytochrome c554, which with a redox potential is -hO.26 V can reduce P865 in 10 /js at room temperature. When electron transfer is interrupted either on the donor or the acceptor side, P865 and 1 recombine to form the spin-polarized triplet state through the radical-pair mechanism. The decay time of P865 at room temperature is 90 ps. 

As in the case of the purple photosynthetic bacteria, the more stable electron acceptor of green filamentous bacteria was first detected using instrumentation with millisecond-time resolution and so the rise and decay kinetics of any earlier electron acceptor(s) would be too fast to be detected. The detection of any earlier electron acceptor would require greater time resolution, such as afforded by picosecond spectroscopy. As a framework for further discussion we write the sequence of the primary photochemical and electron-transfer reactions in green filamentous bacteria as follows ... 

Fig. 11. Electron-transfer schemes for the reaction centers of the green sulfur bacteria (A) and green filamentous bacteria (B). The reaction-center components of the green sulfur bacteria are compared to green-plant photosystem I and those of the green filamentous bacteria are compared to green-plant photosystem II or purple bacteria. The decay times and redox potentials are for Prosihecochloris aestuariiand Chloroflexus aurantiacus. See text lor discussion. Figure adapted from Amesz (1987)...

When electron transfer to the secondary acceptor is disrupted, the separated charges recombine in a few nanoseconds, via the radical pair mechanism, to form the spin-polarized triplet state of the primary donor, P. As shown in Fig. 11, the decay time of P865 in the green filamentous bacterium Cf. aurantiacus is 6 //s at ambient temperature. At 1.2 K it is 75 /js. Reaction centers of Cf. aurantiacus contain two menaquinone molecules, MQa and MQg, which behave the same way as a pair of analogous quinones in purple bacteria and photosystem II. Under non-physiological conditions, MQa recombines with P865 in 60 ms and MQb in 1 s. 

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