Projects

The mechanism and kinetics of electron transfer in isolated D1/D2-cytb559 photosystem (PS) II reaction centers (RCs) and in intact PSII cores have been studied by femtosecond transient absorption and kinetic compartment modeling. For intact PSII, a component of .1.5 ps reflects the dominant energy-trapping kinetics from the antenna by the RC. A 5.5-ps component reflects the apparent lifetime of primary charge separation, which is faster by a factor of 8.12 than assumed so far. The 35-ps component represents the apparent lifetime of formation of a secondary radical pair, and the .200-ps component represents the electron transfer to the QA acceptor. In isolated RCs, the apparent lifetimes of primary and secondary charge separation are .3 and 11 ps, respectively. It is shown (i) that pheophytin is reduced in the first step, and (ii) that the rate constants of electron transfer in the RC are identical for PSII cores and for isolated RCs. We interpret the first electron transfer step as electron donation from the primary electron donor Chlacc D1. Thus, this mechanism, suggested earlier for isolated RCs at cryogenic temperatures, is also operative in intact PSII cores and in isolated RCs at ambient temperature. The effective rate constant of primary electron transfer from the equilibrated RC* excited state is 170.180 ns.1, and the rate constant of secondary electron transfer is 120.130 ns.1.
DOI:10.1073/pnas.0505371103

taxonomy:32046

GO:0030096

The synthesis by organisms of organic chemical compounds, especially carbohydrates, from carbon dioxide (CO2) using energy obtained from light rather than from the oxidation of chemical compounds.
GO:0015979

Chloroplasts are semiautonomous arganelles comprising an envelope formed of two membranes, an aqueous matrix known as stroma, and an extensive system of internal membranes known as thylakoids. All of the light-harvesting and energy-transducing functions are located in the thylakoids." [source: local, PMID:15187262]