The ultrafast behavior of the ferrous heme f from the cytochrome b6f complex of oxygenic photosynthesis
is revealed by means of transient absorption spectroscopy. Benefiting from the use of
microfluidic technologies for handling the sample as well as from a complementary frame-by-frame
analysis of the heme dynamics, the different relaxation mechanisms from vibrationally excited states
are disentangled and monitored via the shifts of the heme a-absorption band. Under 520 nm laser
excitation, about 85% of the heme f undergoes pulse-limited photo-oxidation (o100 fs), with the
electron acceptor being most probably one of the adjacent aromatic amino acid residues. After charge
recombination in 5.3 ps, the residual excess energy is dissipated in 3.6 ps. In a parallel pathway, the
remaining 15% of the hemes directly relax from their excited state in 2.5 ps. In contrast to a vast variety
of heme-proteins, including the homologous heme c1
from the cytochrome bc1 complex, there is no
evidence that heme f photo-dissociates from its axial ligands. Due to its unique binding, with histidine
and an unusual tyrosine as axial ligands, the heme f exemplifies a dependence of ultrafast dynamics on
the structural environment.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)