1. Reduction of pheophytin in the primary light reaction of photosystem II
- Author
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Klimov, V.V., Klevanik, A.V., Shuvalov, V.A., and Krasnovsky, A.A.
- Subjects
Chlorophyll ,Pheophytin ,Chloroplasts ,Light ,Photosystem II ,Biophysics ,Plastoquinone ,Photochemistry ,Photosystem I ,Biochemistry ,chemistry.chemical_compound ,Structural Biology ,Genetics ,Photosynthesis ,Molecular Biology ,Chlorophyll fluorescence ,P700 ,Chemistry ,Pheophytins ,P680 ,Light-harvesting complexes of green plants ,Cell Biology ,Darkness ,Plants ,Kinetics ,Spectrometry, Fluorescence ,Oxidation-Reduction - Abstract
The photochemical reduction of pheophytin and bacteriopheophytin has been shown in vitro [l-3] . In reaction centers of photosynthetic bacteria bacteriopheophytin a [4-91 and bacteriopheophytin b [ 10, 1 l] act as an intermediary electron carrier between bacteriochlorophyll dimer and the ‘primary’ electron acceptor, a complex of ubiquinone and Fe. When the ubiquinone is in the reduced form the photoaccumulation of reduced bacteriopheophytin can be observed [5-111. In various species of green plants 1.5-2.3 molecules of pheophytin have been found per 100 molecules of chlorophyll [ 121 . In photosystem II of green plants the photoreduction of the primary electron acceptor, Q (plastoquinone), is accompanied by a blue shift of absorption bands at 54.5 nm and 685 nm [13,14] which can belong to a bound or aggregated form of pheophytin in reaction centers of photosystem II [ 141. The photoreduction of pheophytin may be observed in photosystem II preparations from pea chloroplasts at 20°C [ 151. In this work a reversible reduction of pheophytin in the primary light reaction of photosystem II in pea subchloroplast particles at redox potentials (Eh) from -50 mV to -550 mV (when Q is in the reduced form) is demonstrated. This photoreaction is observed at -170°C as well as at 20°C and is accompanied by a 2-3 fold decrease in the chlorophyll fluorescence yield.
- Published
- 1977