The light-harvesting function of carotenoids in the cyanobacterial stress-inducible IsiA complex

We present a spectroscopic investigation of the light-harvesting role of carotenoids in aggregates of the IsiA pigment-protein complex of the cyanobacterium Synechocystis PCC 6803. The results show that carotenoids in IsiA transfer energy on the sub-100 fs timescale from the S2 state to chlorophyll to about the same extent as in the related pigment-protein complexes CP43 and CP47. Selective excitation at the red edge of the S2 absorption of the carotenoids shows that echinenone is more efficient in energy transfer to chlorophyll (37%) when compared to the other carotenoid species in the system (22%).