Common Electron Donor Research Articles

Evidence for plastoquinol-cytochrome [formula omitted] reductase as a common electron donor to P700 and cytochrome oxidase in cyanobacteria

Membranes isolated from Nostoc sp. strain MAC and Anacystis nidulans displayed spectral changes in the cytochrome f b region when examined by reduced minus oxidized or dual wavelength spectrophotometry under physiological conditions. The same changes accompanied both light-induced (photosynthetic) and oxygen-induced (respiratory) electron transport. Physiological reduction of the cytochrome f b moiety was abolished after extraction of plastoquinone but reappeared on reconstitution of the depleted membranes with authentic plastoquinone. Moreover, a mutual inhibition of photosynthetic and respiratory activities could be directly demonstrated with the isolated membranes. From the results it is concluded that the membrane-bound plastoquinol-cytochrome f b reductase functions as a common electron donor to both P700 and the cytochrome oxidase in cyanobacteria.

Absorption Spectra of Exciplexes

Absorption spectra of the exciplexes of pyrene, anthracene, biphenyl, and naphthalene with diethylaniline (DEA) as a common electron donor are recorded by applying pulse laser photolysis. The numerous bands appearing in the spectra are analyzed and attributed to transitions from the emitting charge-transfer state, (A−D+), to higher excited charge-transfer states [(A−*D+) and (A−D+*)], as well as to locally excited states [(A*D) and (AD*)]. The results indicate that exciplex absorption spectroscopy may provide a new route to the experimental observation of excited molecular states (of D or A), which are not detectable in the ground state spectra of the corresponding molecules.