Energy transfer and trapping in red-chlorophyll-free photosystem I from Synechococcus WH 7803.

We report for the first time steady-state and time-resolved emission properties of photosystem I (PSI) complexes isolated from the cyanobacterial strain Synechococcus WH 7803. The PSI complexes from this strain display an extremely small fluorescence emission yield at 77 K, which we attribute to the absence of so-called red antenna chlorophylls, chlorophylls with absorption maxima at wavelengths longer than those of the primary electron donor P700. Emission measurements at room temperature with picosecond time resolution resulted in two main decay components with lifetimes of about 7.

Association of chlorophyll a/c(2) complexes to photosystem I and photosystem II in the cryptophyte Rhodomonas CS24.

Photosynthetic supercomplexes from the cryptophyte Rhodomonas CS24 were isolated by a short detergent treatment of membranes from the cryptophyte Rhodomonas CS24 and studied by electron microscopy and low-temperature absorption and fluorescence spectroscopy. At least three different types of supercomplexes of photosystem I (PSI) monomers and peripheral Chl a/c(2) proteins were found. The most common complexes have Chl a/c(2) complexes at both sides of the PSI core monomer and have dimensions of about 17x24 nm.

Phycocyanin sensitizes both photosystem I and photosystem II in cryptophyte Chroomonas CCMP270 cells.

This article presents an investigation of the energy migration dynamics in intact cells of the unicellular photosynthetic cryptophyte Chroomonas CCMP270 by steady-state and time-resolved fluorescence measurements. By kinetic modeling of the fluorescence data on chlorophyll and phycocyanin 645 excitation (at 400 and 582 nm respectively), it has been possible to show the excited state energy distribution in the photosynthetic antenna of this alga. Excitation energy from phycocyanin 645 is distributed nearly equally between photosystem I and photosystem II with very high efficiency on a 100-ps timescale.

Fluorescence quenching of IsiA in early stage of iron deficiency and at cryogenic temperatures.

Cyanobacteria respond to iron deficiency during growth by expressing the isiA gene, which produces a chlorophyll-carotenoid protein complex known as IsiA or CP43'. Long-term iron deficiency results in the formation of large IsiA aggregates, some of which associate with photosystem I (PSI) while others are not connected to a photosystem. The fluorescence at room temperature of these unconnected aggregates is strongly quenched, which points to a photoprotective function.

Protein shape and crowding drive domain formation and curvature in biological membranes.

Folding, curvature, and domain formation are characteristics of many biological membranes. Yet the mechanisms that drive both curvature and the formation of specialized domains enriched in particular protein complexes are unknown. For this reason, studies in membranes whose shape and organization are known under physiological conditions are of great value.

How energy funnels from the phycoerythrin antenna complex to photosystem I and photosystem II in cryptophyte Rhodomonas CS24 cells.

We report an investigation of energy migration dynamics in intact cells of the photosynthetic cryptophyte Rhodomonas CS24 using analyses of steady-state and time-resolved fluorescence anisotropy measurements. By fitting a specific model to the fluorescence data, we obtain three time scales (17, 58, and 113 ps) by which the energy is transferred from phycoerythrin 545 (PE545) to the membrane-associated chlorophylls (Chls). We propose that these time scales reflect both an angular distribution of PE545 around the photosystems and the relative orientations of the donor dihydrobiliverdin (DBV) bilin and the acceptor Chl.

Excitation energy transfer and charge separation in photosystem II membranes revisited.

We have performed time-resolved fluorescence measurements on photosystem II (PSII) containing membranes (BBY particles) from spinach with open reaction centers. The decay kinetics can be fitted with two main decay components with an average decay time of 150 ps. Comparison with recent kinetic exciton annihilation data on the major light-harvesting complex of PSII (LHCII) suggests that excitation diffusion within the antenna contributes significantly to the overall charge separation time in PSII, which disagrees with previously proposed trap-limited models.