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77 K fluorescence quenching induced by reduction of Photosystem I primary electron acceptors in a cyanobacterium

1986; Elsevier BV; Volume: 848; Issue: 3 Linguagem: Inglês

10.1016/0005-2728(86)90210-0

1879-2650

Jean‐Claude Duval, Jean‐Claude Thomas, Yves Choquet,

Spectroscopy and Quantum Chemical Studies

A Pseudanabaena strain isolated in our laboratory exhibited a large amount of a 710 nm chlorophyll form, associated with Photosystem I, the chromophore of which was found to be parallel to the membrane plane as shown by linear dichroism measurements. Whole cells, thylakoid vesicles and Photosystem I particles obtained after digitonin treatment presented a particular 77 K fluorescent component at 750 nm (F750):a high initial level of fluorescence (F0) was obtained when samples were frozen in the dark; illumination induced a decrease to a low level (FL). Kinetic analysis showed that this decrease was biphasic, with a first phase 3-times faster than the second one. F0FL ratio was about 3. Action spectra demonstrate the origin and properties of chlorophyll 710. By poising Photosystem I electron acceptors at different oxidoreduction states, and from experiments with ferricyanide, we conclude that the fluorescence at 750 nm originates from a chlorophyll form absorbing at 710 nm in a close relation to P-700 and that its kinetics can be used to evaluate Photosystem I primary electron acceptor pools.