GENERATION OF TRIPLET AND CATION-RADICAL BACTERIOCHLOROPHYLL A IN CAROTENOIDLESS LH1 AND LH2 ANTENNA COMPLEXES FROM RHODOBACTER SPHAEROIDES

The assembly of the carotenoid (Car) and bacteriochlorophyll (BChl) molecules in the LH2 antenna complexes of R. acidophila 11050 and Rs. molischianum has been determined by X-ray crystallography [1,21: a pair of B850 BChl molecules which is sandwiched by the a and p peptides and by two Car molecules forms a circular aggregate like the blades of a turbine, the distance between the B850 BChl molecules between the neighboring repeating subunits being closer than that within the same subunit. Although extensive experimental and theoretical investigations have been carried out to understand the implication of this pigment assembly in relation to the light-harvesting function of Car [3], the photo-protective function of Car in the light-harvesting complex (LHC) has not been revealed.