Abstract
By introducing derivative transient absorption spectroscopy, we obtain rate constants for backward and forward energy transfer between LH1 and LH2 complexes in purple bacterial membranes. We find that backward energy transfer is strongly reduced in membranes grown under low irradiation conditions, compared to high light grown ones. We conclude that backward energy transfer is managed actively by the bacteria to avoid LH1 exciton deactivation under high irradiation conditions. The analytical method is generally applicable to excitonically coupled systems.
Highlights
Purple bacteria are excellent model systems for investigating the basic mechanisms of photosynthetic light harvesting [1]
We find that backward energy transfer is strongly reduced in membranes grown under low irradiation conditions, compared to high light grown ones
Two light-harvesting (LH) pigment-protein complexes are present in the photosynthetic unit: LH2 contains a ring of 9 monomeric bacteriochlorophyll a (Bchl a) and 9 pairs of excitonically coupled Bchl a molecules, while LH1 contains a ring with 18 pairs of coupled Bchl a and the reaction center (RC), where charge separation takes place
Summary
Purple bacteria are excellent model systems for investigating the basic mechanisms of photosynthetic light harvesting [1]. By introducing derivative transient absorption spectroscopy, we obtain rate constants for backward and forward energy transfer between LH1 and LH2 complexes in purple bacterial membranes. We find that backward energy transfer is strongly reduced in membranes grown under low irradiation conditions, compared to high light grown ones.
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