Ultrafast chlorophyll b-chlorophyll a excitation energy transfer in the isolated light harvesting complex, LHC II, of green plants. Implications for the organisation of chlorophylls.
The excitation energy transfer between chlorophyll b (Chl b) and chlorophyll a (Chl a) in the isolated trimeric chlorophyll-a/b-binding protein complex of spinach photosystem 2 (LHC II) has been studied by femtosecond spectroscopy. In the main absorption band of Chl b the ground state recovery consists of two components of 0.5 ps and 2.0 ps, respectively. Also in the Chl a absorption band, at 665 nm, the ground state recovery is essentially bi-exponential. In this case is, however, the fastest relaxation lifetime is a 2.0 ps component followed by a slower component with a lifetime in the order of 10-20 ps. In the Chl b absorption band a more or less constant anisotropy of r = 0.2 was observed during the 3 ps the system was monitored. In the Chl a absorption band there was, however, a relaxation of the anisotropy from r = 0.3 to a quasi steady state level of r = 0.18 in about 1 ps. Since the 0.5 ps component is only seen upon selective excitation of Chl b we assign this component to the energy transfer between Chl b and Chl a. The other components most likely represents redistribution processes of energy among spectrally different forms of Chl a. The energy transfer process between Chl b and Chl a can well be explained by the Förster mechanism which also gives a calculated distance of 13 A between interacting chromophores. The organisation of chlorophylls in LHC II is discussed in view of the recent crystal structure data (1991) Nature 350, 130].
Pålsson
L O
LO
Department of Physical Chemistry, University of Umeå, Sweden.
Spangfort
M D
MD
Gulbinas
V
V
Gillbro
T
T
D002734:Chlorophyll / Q000378:metabolism*; D000077194:Chlorophyll A; D004735:Energy Transfer; D005454:Fluorescence Polarization; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*; D010944:Plants / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D002734:Chlorophyll; C037184:chlorophyll b; D000077194:Chlorophyll A