Steensgaard D B, van Walree C A, Permentier H, Bañeras L, Borrego C M, Garcia-Gil J, Aartsma T J, Amesz J, Holzwarth A R
Max-Planck-Institut für Strahlenchemie, Stiftstrasse 34-36, D-45470, Mülheim an der Ruhr, Germany.
Biochim Biophys Acta. 2000 Feb 24;1457(1-2):71-80. doi: 10.1016/s0005-2728(99)00112-7.
We have studied energy transfer in chlorosomes of Chlorobium limicola UdG6040 containing a mixture of about 50% bacteriochlorophyll (BChl) c and BChl d each. BChl d-depleted chlorosomes were obtained by acid treatment. The energy transfer between the different pigment pools was studied using both steady-state and time-resolved fluorescence spectroscopy at room temperature and low temperature. The steady-state emission of the intact chlorosome originated mainly from BChl c, as judged by comparison of fluorescence emission spectra of intact and BChl d-depleted chlorosomes. This indicated that efficient energy transfer from BChl d to BChl c takes place. At room temperature BChl c/d to BChl a excitation energy transfer (EET) was characterized by two components of 27 and 74 ps. At low temperature we could also observe EET from BChl d to BChl c with a time constant of approximately 4 ps. Kinetic modeling of the low temperature data indicated heterogeneous fluorescence kinetics and suggested the presence of an additional BChl c pool, E790, which is more or less decoupled from the baseplate BChl a. This E790 pool is either a low-lying exciton state of BChl c which acts as a trap at low temperature or alternatively represents the red edge of a broad inhomogeneous absorption band of BChl c. We present a refined model for the organization of the spatially separated pigment pools in chlorosomes of Cb. limicola UdG6040 in which BChl d is situated distal and BChl c proximal with respect to the baseplate.
