EPR study of structure of the primary reactants in photosystem I (PSI)
- Argonne National Lab., IL (United States)
In the PSI photosynthetic reaction center, photoinduced electron transfer proceeds from the excited primary donor P{sub 700}, through a series of electron acceptors. Phylloquinone [K{sub 1}] is believed to be the second electron acceptor, [A{sub 1}]. The electron spin polarized EPR signals of the interacting P{sup +}{sub 700}A{sub 1}-pair can be used as a probe of the structure of the A{sub 1} binding site. We have examined the time-resolved EPR signals in whole cell and isolated PSI protein preparations of the deuterated cyanobacterium Synnechococcus lividus, as well as preparations in which the deuterated A{sub 1} has been exchanged with protonated K{sub 1}, by incubation of the PSI preparation in the precess of an excess of K{sub 1}. The observation of EPR signals evolving from P{sup +}{sub 700}A{sub 1}{sup -} in the {open_quotes}exchanged{close_quotes} preparations implies that exchange via incubation results in the successful replacement of the endogenous quinone, and is a demonstration that the native A{sub 1} acceptor can be exchanged without prior extraction of K{sub 1}. The effects of incubation time, temperature, and light on K{sub 1} exchange, and possible reasons for the exchangeability of the A{sub 1} acceptor in PSI will be discussed. We extract structural information about the interacting P{sup +}{sub 700}A{sub 1}{sup -} pair from their transient EPR signals observed under the various exchange conditions.
- Research Organization:
- Argonne National Laboratory (ANL), Argonne, IL
- DOE Contract Number:
- W-31109-ENG-38
- OSTI ID:
- 215141
- Report Number(s):
- CONF-950801--
- Country of Publication:
- United States
- Language:
- English
Similar Records
EPR evidence that the photosystem I acceptor A/sub 1/ is a quinone molecule
Contribution of vitamin K1 to the electron spin polarization in spinach photosystem I