Download Photosynthesis in cyanobacteria and plants Simple Z Scheme for

Photosynthesis in cyanobacteria and plants
Plants and cyanobacteria use the reducing power generated by the
light-driven oxidation of H2O to produce NADPH
this is an uphill battle and photosynthesis therefore requires at least 810 photons of visible light to produce one molecule of oxygen
Two processes are involved in photosynthesis (usually depicted in form
of a Z scheme)
Both processes are mediated by the action of two RCs (which
essentially act in series): These are called PS I and PS II
PS I: generates a strong reductant capable of reducing NADP+
PS II: generates a strong oxidant capable of oxidizing water to O2
1
Simple Z Scheme for photosynthesis in plants and cyanobacteria
DCMU is a herbicide
which interrupts
electron flow from PS
II to cyt f
2
1
Another Z Scheme
3
4
2
The Thylakoid membrane and its components
Stroma
Thylakoid
lumen
5
Q cycle
Q
QH2
6
3
Plastocyanin (PC)
PC is a mobile electron carrier transferring electrons from cytochrome
b6f complex to PS I
PC is a blue copper protein
7
Structure of Plastocyanin
8
4
Environment of the Cu(II) in blue copper
proteins is highly strained (entatic state)
9
EPR (Electron paramagnetic resonance)
spectroscopy
Splitting in external magnetic fields
10
5
EPR spectroscopy of Cu(II) proteins
The unpaired electron in Cu(II) is delocalized over the thiolate sulfur of
cysteine in blue copper centres (this is why the hyperfine splitting in the
protein is less than in a normal Cu complex)
11
Arrangement of cofactors in the RC subunits of PS II
12
6
13
14
7
15
The Oxygenevolving complex
(OEC)
16
8
17
18
9
Previously proposed structure of the Mn4 cluster in OEC
New structures
2011
(1.9 Å res.)
19
2009
Ligand environment of the OEC (1.9 Å structure)
Kawakami, K. et al. (2011) J. Photochem. Photobiol. B: Biol. 104, 9-18.
20
10
Kawakami, K. et al. (2011) J. Photochem. Photobiol. B: Biol. 104, 9-18.
21
Revised mechanism of OEC
Siegbahn, P.E.M. (2009) Acc.
Chem. Res. 42, 1871-1880.
22
11
Model complexes
23
24
12
A working model compound
25
Dark reactions (Calvin cycle)
26
13