ENERGY-TRANSFER DYNAMICS IN 3 LIGHT-HARVESTING MUTANTS OF RHODOBACTER-SPHAEROIDES - A PICOSECOND SPECTROSCOPY STUDY

Picosecond absorption spectroscopy has been used to investigate energy-transfer dynamics within the LH 1 and LH2 light-harvesting complexes of three mutants of Rhodobacter sphaeroides. We demonstrate that both complexes are inhomogeneous; each contains a specialized pigment pool which absorbs maximally at a longer wavelength. Within LH2 (mutant NF57), Bchl850 transfers energy to Bchl870 in 39 ± 9 ps; within LH1 (mutants M21 and M2192), energy is transferred from Bchl875 to Bchl896 in 22 ± 4 and 35 ± 5 ps, respectively. Examination of the decay of induced absorption anisotropy indicates that each of these specialized pools exists in a state which is highly organized with respect to the remainder of the pigments. Such an arrangement may facilitate and direct energy migration toward the reaction center. © 1990, American Chemical Society. All rights reserved.