Abstract— The dark decay kinetics of excited phototraps in chromatophores prepared from Rhodospirillum rubrum have been quantitatively measured under two different conditions where a direct return of the electron(s) from ubiquinone to the primary donor bacteriochlorophyll cation radical is expected. One of these experimental conditions was with a frozen sample (whole cells, chromatophores, and extracted chromatophores) at 77 K, while the other was a room temperature measurement of a sample of chromatophores from which the loosely bound ubiquinone was first removed by extraction with organic solvents. Results with the latter system were also compared to those obtained with chromatophores plus 1 mM o‐phenanthroline. In all cases the kinetics of charge recombination were not pseudo‐first order but showed a biphasic pattern. The data at low temperature could be exactly fit by assuming that two major pseudo‐first order processes were occurring with half times of 6.5 and 19 ms, 22% decaying by the faster process and 78% by the slower process. Both types of experiments at room temperature could also be fit by assuming two major pseudo‐first order processes were occurring, but with somewhat slower half times, 22 and 59 ms. In this case, 20% decayed by the faster process and 80% by the slower process. An equation was developed to fit the data assuming that one ubiquinone molecule was the electron acceptor for two donor units (the duplex model), the dark decay thus taking place in two sequential steps with 50% of the oxidized donor units becoming reduced in each step. The experimental data could be exactly fit using this equation and the above parameters. The data are viewed as best supporting the duplex model for explaining primary photochemical events in these bacteria.
|Original language||English (US)|
|Number of pages||7|
|Journal||Photochemistry and Photobiology|
|State||Published - Jan 1 1978|
ASJC Scopus subject areas
- Physical and Theoretical Chemistry