The role of metal ions in
photosynthesis
The photosynthesis
Solar energy – chemical energy
The green plants produce ~ 1 g glucose every
hour per square meter of leaf surface. This
means that photosynthesis is the highest
volume biochemical process in the Earth, as
approximately 200 billion ton carbohydrate
equivalent is formed per year in this reaction,
although only less than 1% of the radiation
reached the Earth is utilised in the
photosynthesis.
~10 Nobel prize
Photosynthesis
Photosynthesis
Photosynthesis
Photosynthesis
Absorption of light and transfer in the photosynthetic
system – The photosynthetic reaction centres
The electron transport chain between the two photosystems
Mn-catalysed oxidation of water to dioxygen (OEC)
The role of the ribulose 1,5-diphosphate in the photosystem
Evolution – vs. Future outlooks
Photosynthesis
Absorption of light and transfer in the photosynthetic
system – The photosynthetic reaction centres
The electrontransport chain between the two photosystems
Mn-catalysed oxidation of water to dioxygen (OEC)
The role of the ribulose-1,5-diphosphate in the photosystem
Evolution – vs. Future outlook
Photosynthesis – utilization of sunlight
Photosynthesis – utilization of sunlight
Pigments of photosynthesis
Chlorophyll A
Pigments of photosynthesis
The „antenna” of photosynthesis
Structurisation of the pigment
materials
in
the
thylakoid
membrane in the monomeric
antenna
complex
of
the
photosystem II (CP43 and CP47 in
the antenna complex and D1/D2 in
the reaction centre) A and B Figs.
show different views.
Stroma
Sztróma
Lumen
Science 2004, 303, 1831
The „antenna” of photosynthesis
A
Structurisation of the pigment
materials in the thylakoide
membrans in the antenna
complexes of photosystem I. A
and B Figs. show different
views.
B
Current Opinion in Structural Biology 2002, 12, 244
Transport of the photon energy by resonance transfer
The positive characteristics of magnesium ions in the
photosynthesis
Assure the spatial arrangement of the chlorophyll molecules. The Mg2+ion is perfect for this role: because its size is optimal to form stable
complex with the tetrapyrrole ring, furthermore it prefers to form
complexes with coordination number six.
The Mg2+ ion forms only weak spin-orbit coupling with the excited state
of the tetrapyrrole ring, and thus it hinders the transfer of the energy of
light in the forms of fluorescence or heat.
The Mg2+ ion in contrast with most of the transition metal ions can not
redox react with the surronding ligands and thus the photosynthetic
reaction centres are defended from the unwanted irreversible
decomposition.
Photosynthesis - photosystems
Photosynthesis - photosystems
Photosyntesis – photosystems II
Structurisation of the PS II dimer pigment-protein complex in the thylakoid membrane
Science 2004, 303, 1831
ATP synthesis
Photosynthesis
Absorption of light and transfer in the photosystem – The
photosynthetic reaction centres
The electron transport chain between the two photosystems
Mn catalysed oxidation of water to dioxygen (OEC)
The role of ribulose 1,5-diphosphate in the photosystem
Evolution – vs. Future outlook
Electrontransfer metalloproteins
1.) Iron-sulphur proteins
(Ferredoxin):
Electrontransfer metalloproteins
2.) Cytochromes:
Hem a
Hem c
Cytochrome c
Electrontransfer metalloproteins
3.) Blue copper proteins (Plastocyanin):
The photosynthetic electron transport Z scheme
Elements of the photosynthetic electrontransport
bicarbonate
bikarbonátion
-karotin
Relative arrangement of the molecules participating in the primary electrontransport
processes of PS II system.
Science 2004, 303, 1831
Elements of the photosynthetic electron transport
Schematic picture of the b6f complex of the eucaryota photosynthetic
electrontransport system.
The long range electron transfer and transport
systems
Schematic picture of a part of the eucariote photosynthetic
electrontransport system (cytochrome f → plastocyanin → P700).
Reduction of NADP+
+H+
+2e-
Photosynthesis
Absorption of light and transfer in the photosystem – The
photosynthetic reaction centres
The electron transport chain between the two photosystems
Mn-catalysed oxidation of water to dioxygen (OEC)
The role of ribulose 1,5 diphosphate in photosystem
Evolution – vs. Future outlook
Oxidation of water
Oxidation of water
+1,2
Suggested structures of the OEC (WOC)
Coordination Chemistry Reviews 2008, 252
OEC models from the same X-ray structures
(A)
(B)
Coordination Chemistry Reviews 2008, 252
Schematic figure of the OEC catalytic centre
The amino acids indicated by
different colours belong to
different protein subunits: yellow D1, orange - D2 and green - CP43.
Science 2004, 303, 1831
Schematic figure of oxidation of the water
2H2O
S0
h
S1
h
2Mn3+
2Mn4+
3Mn3+
1Mn4+
H+
40ms
e-
e-
e-
e-
S2
h
h
S4
S3
1Mn3+
3Mn4+
1Mn3+
3Mn4+
H+
100ms 250ms
O2
1Mn3+
3Mn4+
2H+
~1ms
OEC (Oxygen Evolving Complex): The lifetime, the composition of the complex and
evolution of protons and electrons in the oxidation steps of water.
A proposed mechanism of the stepwise oxidation of water
(The question marks indicates that the Mn-Mn distances are not known.)
Chemical Reviews 1996, 96, 2947
A proposed mechanism of the stepwise oxidation of water
Biochimica et Biophysica Acta 2001, 1503
A proposed mechanism of the stepwise oxidation of water
Coordination Chemistry Reviews 2008, 252
Proposed structure of OEC (WOC) - 2011
Nature 2011, 473, 55
Favourable characteristics of the manganase ions in
the photosynthesis
(i) Versatility in the stable or metastable oxidation states of manganese:
MnII, MnIII, MnIV, MnVI, MnVII.
(ii) Labile coordination of the ligands.
(iii) Propensity to form high spin complexes.
(iv) The freshly formed mixed valence oxides MnO2–x×nH2O catalyses
efficiently the disproportionation of hydrogene-peroxide, in which
oxygen is also formed. Such oxide-hydroxide compounds might also be
present, when photosynthesis was evolved.
(v) Besides the metabolism of oxygen, the Mnn+ ions occur in other
enzymes, such as the Mn containing superoxide dismutases as well as
catalases and peroxidases.
Hydrophil and hydrophob channels around the OEC
(3)
(2)
(1)
1. O2 channel; 2 and 3. hydrophil channels for the substrate and the proton.
Coordination Chemistry Reviews 2008, 252
Modeling the water flow around the OEC
Biochemistry, 2010, 49, 1873
Photosynthesis
Absorption of light and transfer in the photosystem – The
photosynthetic reaction centre
The electron transport chain between the two photosystems
Mn catalysed oxidation of water to dioxygen (OEC)
The role of ribulose 1,5-diphosphate in the photosystem
Evolution – vs. Future outlook
Reactions of the dark process
Reactions of the dark process
Schematic picture of the CO2 fixation catalysed by ribulose 1,5 diphosphate
carboxylase enzyme.
Reactions of the dark process
CH2O P
CH2O P
C O
HC OH
HC OH
CH2O P
O
CO2
C
O
C OH
C OH
HC OH
CH2O P
O
-
O
H O
H
CH2O P
CH2O P
C C OH
C
O
HC OH
2
C OH
O
C
O-
CH2O P
Schematic picture of the CO2 fixation catalysed by ribulose 1,5 diphosphate
carboxylase enzyme.
Structure of the ribulose 1,5 diphosphate carboxylase
X-ray structure of the ribulose 1,5-diphosphate carboxylase enzyme C. Reinhardtii
green algae. The L subunits are indicated by blue and green, while the S subunits
by yellow colour.
Journal of Molecular Biology 2002, 316, 679
Active centre of the ribulose 1,5-diphosphate carboxylase
Active centre of the ribulose 1,5-diphosphate carboxylase enzyme of C. Reinhardtii
green algae in the presence of a model substrate.
Journal of Molecular Biology 2002, 316, 679
Photosynthesis
Absorption of light and transfer in the photosystem – The
photosynthetic reaction centre
The electron transport chain between the two photosystems
Mn catalysed oxidation of water to dioxygen (OEC)
The role of ribulose 1,5-diphosphate in the photosystem
Evolution – vs. Future outlook
Evolution of photosynthesis
Green sulphur bacteria:
Reaction centre of the purple bacteria
The photosynthesis
Artificial photosynthesis
Artificial photosynthesis
Coordination Chemistry Reviews 252 (2008) 444
Artificial photosynthesis
Coordination Chemistry Reviews 252 (2008) 456
Photosynthetic car?