Energy transfer and spectral dynamics of the three lowest energy Q(y)-states of the Fenna-Matthews-Olson antenna complex

Temperature-dependent (1.8-10 K) spectral hole burning results are presente d for the three lowest Q(y)-states of the Fenna-Matthews-Olson (FMO) bacter iochlorophyll a antenna complex of Chlorobium tepidum that contribute to th e 825 nm absorption band. Both holewidth and hole growth kinetic data are p resented. The data indicate that the three states he at 823, 825, and 827 n m and, furthermore, that they are associated with the lowest energy state o f the subunit of the FMO trimer; Structural heterogeneity results in the th ree states being energetically inequivalent. The time constants for downwar d energy transfer from the 823 and 825 nm states are 37 and 117 ps, respect ively. It is argued that the time constants for the 823 nm --> 825 and 823 nm --> 827 nm pathways are 117 and 54 ps, respectively. The dispersive hole growth kinetic data for the three states obtained at 1.8 and 8.0 K are sho wn to be consistent with the excited-state lifetimes and homogeneous widths of the zero-phonon absorption lines. Analysis of the data leads to a lifet ime of 2 ns for. the 827 nm state. The temperature dependencies of the zero -phonon lines associated with this and the other two states are identical a nd characteristic of coupling to the two-level systems of the protein.