4
A. Trebst
plastoquinone QB. After two excitations the plastoquinol formed has taken
up two protons from the matrix space. The essential components of the
primary charge separation are a chlorophyll a dimer P 680, two monomeric
chlorophylls and two pheophytins. These six compounds are oriented
symmetrically in the membrane and are bound to two protein subunits of
photosystem II, called the D1 and D2 polypeptide. The reaction center P 680
appears to be connected functionally to only one monomeric chlorophyll
and one pheophytin. This is called the active arm of electron flow from the
reaction center to QA.
+ZH+ lumen
Tyrosin161 = Yz
Dl
~fast
> ~
Tyrosin161 = Y D
D2
monomeric chlorophyll
.
Fe
reaction active arID ~ pheophy-tm---j>QA ~ OB
_ _ _
Dl
center
P680~
'~ pheophytin
ZH+
.{,
matrix
plastoquinol
inactive arm
DZ
The second symmetrical arm with the other monomeric chlorophyll and
the second pheophytin remains inactive (Fig. 1.1).
The tilt of the transmembrane helices of the two subunits (discussed
below) places the QA side on the D2 protein exactly above the pheophytin
Lumen
Fig. 1.1. The integral membrane complex of photo system II oriented in the thylakoid
membrane. Several transmembrane polypeptide units carry the prosthetic groups: the
reaction center P680, pheophytin (Ph) and Fe on the D1 and D2 protein, OA on the D2
and OB on the D1 protein, antenna chlorophylls on the CP 43 and CP 47 kDa polypeptides.
Managanese is attached on the D11D2 proteins, stabilized by the peripheral polypeptides
of 33, 16, und 10 kDa and by Ca and Cl ions. The role of the cytochrome b559 is not clear,
nor is that of several other polypeptides. Tyrosin 161 in the D1 protein is the electron
donor Y z between the manganese cluster and P 680. A much slower donor tyrosin Y D is in
the D2 protein. After the charge separation of excited P680 , the electron travels via
pheophytin and a monomeric chlorophyll on the Dl protein to OA bound to the D2
protein; this is called the active arm. The symmetrical groups on the D2 protein remain
inactive
A. Trebst
plastoquinone QB. After two excitations the plastoquinol formed has taken
up two protons from the matrix space. The essential components of the
primary charge separation are a chlorophyll a dimer P 680, two monomeric
chlorophylls and two pheophytins. These six compounds are oriented
symmetrically in the membrane and are bound to two protein subunits of
photosystem II, called the D1 and D2 polypeptide. The reaction center P 680
appears to be connected functionally to only one monomeric chlorophyll
and one pheophytin. This is called the active arm of electron flow from the
reaction center to QA.
+ZH+ lumen
Tyrosin161 = Yz
Dl
~fast
> ~
Tyrosin161 = Y D
D2
monomeric chlorophyll
.
Fe
reaction active arID ~ pheophy-tm---j>QA ~ OB
_ _ _
Dl
center
P680~
'~ pheophytin
ZH+
.{,
matrix
plastoquinol
inactive arm
DZ
The second symmetrical arm with the other monomeric chlorophyll and
the second pheophytin remains inactive (Fig. 1.1).
The tilt of the transmembrane helices of the two subunits (discussed
below) places the QA side on the D2 protein exactly above the pheophytin
Lumen
Fig. 1.1. The integral membrane complex of photo system II oriented in the thylakoid
membrane. Several transmembrane polypeptide units carry the prosthetic groups: the
reaction center P680, pheophytin (Ph) and Fe on the D1 and D2 protein, OA on the D2
and OB on the D1 protein, antenna chlorophylls on the CP 43 and CP 47 kDa polypeptides.
Managanese is attached on the D11D2 proteins, stabilized by the peripheral polypeptides
of 33, 16, und 10 kDa and by Ca and Cl ions. The role of the cytochrome b559 is not clear,
nor is that of several other polypeptides. Tyrosin 161 in the D1 protein is the electron
donor Y z between the manganese cluster and P 680. A much slower donor tyrosin Y D is in
the D2 protein. After the charge separation of excited P680 , the electron travels via
pheophytin and a monomeric chlorophyll on the Dl protein to OA bound to the D2
protein; this is called the active arm. The symmetrical groups on the D2 protein remain
inactive