1 Dynamics in Photosystem II
Structure and Function
A. Trebst
1.1 Introduction
In photosynthetic electron flow, light supplies the driving force for NADP
reduction, oxygen evolution and ATP formation. Three integral protein
complexes in the thylakoid membrane - photo system I, photo system II,
and the cytochrome b6/f complex - with several peripheral polypeptides
attached, bind the pigments and redox systems that participate in electon
flow: chlorophylls in the antenna and the reaction centers of the two photosystems, pheophytin in PS II, plastoquinone bound to PS II and in the
quinone pool and menaquinone to PS I, iron in iron sulfur centers (of the
Fe2S2 and Fe4S4 type: of very low potential in ferredoxin and the acceptor
site of PS I, and of high potential in the Rieske Fe2S2 center in the cytochrome b 6 /f complex) and in histidine-bound Fe in PS II, iron in the hemes
in cytochromes f and b6 in the blf complex and in bss9 in PS II, copper in
plastocyanin, FAD in the Fd-NADP reductase and a manganese cluster in
PS II. The proteins bind and orient these components in the membrane,
thus allowing transmembrane vectorial electron flow. Each integral membrane complex with an average of about 350 kDa size contains several
polypeptide subunits from very low molecular weight (4 kDa) up to 64 kDa.
Peripheral hydrophilic proteins are attached to the membrane proteins or
are soluble in the matrix (ferredoxin) or lumen (plastocyanin) space. For
recent reviews on the functional structure of PS II see Barber (1987, 1992).
1.2 Function of Photosystem II
Photosystem II oxidizes water to evolve oxygen and provides electrons and
protons. The energy is conserved in reducing equivalents (plastoquinol) and
in a proton motive force. The protons are released in the inner lumen of
the thylakoid and contribute to the driving force for ATP synthesis. The
electrons are transported across the membrane after the light-dependent
charge separation in the (excited) reaction center P680 via pheophytin to the
first bound plastoquinone QA. Then the electron is passed on to the second
Structure and Function
A. Trebst
1.1 Introduction
In photosynthetic electron flow, light supplies the driving force for NADP
reduction, oxygen evolution and ATP formation. Three integral protein
complexes in the thylakoid membrane - photo system I, photo system II,
and the cytochrome b6/f complex - with several peripheral polypeptides
attached, bind the pigments and redox systems that participate in electon
flow: chlorophylls in the antenna and the reaction centers of the two photosystems, pheophytin in PS II, plastoquinone bound to PS II and in the
quinone pool and menaquinone to PS I, iron in iron sulfur centers (of the
Fe2S2 and Fe4S4 type: of very low potential in ferredoxin and the acceptor
site of PS I, and of high potential in the Rieske Fe2S2 center in the cytochrome b 6 /f complex) and in histidine-bound Fe in PS II, iron in the hemes
in cytochromes f and b6 in the blf complex and in bss9 in PS II, copper in
plastocyanin, FAD in the Fd-NADP reductase and a manganese cluster in
PS II. The proteins bind and orient these components in the membrane,
thus allowing transmembrane vectorial electron flow. Each integral membrane complex with an average of about 350 kDa size contains several
polypeptide subunits from very low molecular weight (4 kDa) up to 64 kDa.
Peripheral hydrophilic proteins are attached to the membrane proteins or
are soluble in the matrix (ferredoxin) or lumen (plastocyanin) space. For
recent reviews on the functional structure of PS II see Barber (1987, 1992).
1.2 Function of Photosystem II
Photosystem II oxidizes water to evolve oxygen and provides electrons and
protons. The energy is conserved in reducing equivalents (plastoquinol) and
in a proton motive force. The protons are released in the inner lumen of
the thylakoid and contribute to the driving force for ATP synthesis. The
electrons are transported across the membrane after the light-dependent
charge separation in the (excited) reaction center P680 via pheophytin to the
first bound plastoquinone QA. Then the electron is passed on to the second