Picosecond Energy Transfer Kinetics between Different Pigment Pools in Chlorosomes from the Green Bacterium Chloroflexus Aurantiacus

Abstract

Chloroflexus aurantiacus a thermophilic green bacterium, contains at least four different bacteriochlorophyll (BChI)-complexes which are coupled in a specific way to optimize the energy transfer from the main antenna, the so-called chlorosome, to the reaction center (1–4). Chlorosomes contain about 1000 – 16000 BChI c molecules (5) which are believed to be organized in rod-like substructures (6). Two BCh1 a-protein complexes function as intermediate pigment pools. The BChl a790 complex is believed to be the first and the B 806–866 complex the second one in the energy transfer chain from the chlorosome to the reaction center (1,2). Energy transfer studies have been carried out in the past using steady state measurements (1,2), as well as picosecond absorption (7), and picosecond fluorescence measurements (2,8). The samples used were either membranes and whole cells or isolated chlorosomes containing BChI a790. We have recently reported on the preparation of chlorosomes free from bound BCh1 a790 (9). In this report we compare the energy transfer kinetics in both types of chlorosomes.