Abstract

The core (LH-1) antenna complexes of purple non-sulfur bacteria are membrane-bound light-harvesting complexes which enclose the reaction centers.¹ They can be described as circular aggregates of a basic subunit (typically 12 per LH-1 complex¹) consisting of two helical polypeptides (α and β) and two bacteriochlorophyll-a (BChla) chromophores. Under special conditions, the LH-1 complex can be reversibly dissociated into such subunits, which display spectral properties consistent with a those of strongly coupled BChla dimer.¹ A crucial yet unresolved issue concerns the extent of interaction between neighbouring subunits in the intact complex, i.e. the degree to which dimeric properties are retained in the functional aggregate. It remains debated as to whether the electronic states are delocalized over several pigments,² or may be viewed as being localized on individual dimers or tetramers.³ Knowledge of the exciton level structure and dynamics within the subunit, and the effects of aggregation on these properties is clearly required to establish an understanding of the mechanism of energy migration. We report here the preliminary results from studies of the femtosecond transient kinetics of the B820 subunit (which incorporates one dimer of BChla) from the LH-1 complex of Rhodospirillum rubrum G9.

© 1996 Optical Society of America