The role of metal ions in photosynthesis

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

Solar energy – chemical energy

The 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

Photosynthesis – utilization of sunlight

Photosynthesis – utilization of sunlight

Pigments of photosynthesis

Chlorophyll A

Pigments of photosynthesis

Sztróma

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.

The „antenna” of photosynthesis

Science 2004, 303, 1831

Stroma

Lumen

Structurisation of the pigment materials in the thylakoide membrans in the antenna complexes of photosystem I. A and B Figs. show different views.

A

B

Current Opinion in Structural Biology 2002, 12, 244

The „antenna” of photosynthesis

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

Structurisation of the PS II dimer pigment-protein complex in the thylakoid membrane

Science 2004, 303, 1831

Photosyntesis – photosystems II

ATP synthesis

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

Photosynthesis

1.) Iron-sulphur proteins (Ferredoxin):

Electrontransfer metalloproteins

2.) Cytochromes:

Hem a Hem c

Cytochrome c

Electrontransfer metalloproteins

3.) Blue copper proteins (Plastocyanin):

Electrontransfer metalloproteins

The photosynthetic electron transport Z scheme

Relative arrangement of the molecules participating in the primary electrontransport processes of PS II system.

bikarbonátion

-karotin

Science 2004, 303, 1831

Elements of the photosynthetic electrontransport

bicarbonate

Schematic picture of the b6f complex of the eucaryota photosynthetic electrontransport system.

Elements of the photosynthetic electron transport

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-

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

Photosynthesis

Oxidation of water

+1,2

Oxidation of water

Suggested structures of the OEC (WOC)

Coordination Chemistry Reviews 2008, 252

OEC models from the same X-ray structures

Coordination Chemistry Reviews 2008, 252

(A) (B)

The amino acids indicated by different colours belong to different protein subunits: yellow - D1, orange - D2 and green - CP43.

Schematic figure of the OEC catalytic centre

Science 2004, 303, 1831

2H2O S0 S1 S2 S3 S4 O2h h h h

3Mn3+

1Mn4+2Mn3+

2Mn4+1Mn3+

3Mn4+

1Mn3+

3Mn4+1Mn3+

3Mn4+

e- e- e- e-

H+ H+ 2H+

40ms 100ms 250ms ~1ms

OEC (Oxygen Evolving Complex): The lifetime, the composition of the complex and evolution of protons and electrons in the oxidation steps of water.

Schematic figure of oxidation of the 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

A proposed mechanism of the stepwise oxidation of water

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.

1. O2 channel; 2 and 3. hydrophil channels for the substrate and the proton.

Hydrophil and hydrophob channels around the OEC

Coordination Chemistry Reviews 2008, 252

(1)

(3)

(2)

Modeling the water flow around the OEC

Biochemistry, 2010, 49, 1873

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

Photosynthesis

Reactions of the dark process

Schematic picture of the CO2 fixation catalysed by ribulose 1,5 diphosphate carboxylase enzyme.

Reactions of the dark process

Schematic picture of the CO2 fixation catalysed by ribulose 1,5 diphosphate carboxylase enzyme.

CH2O

C

HC

HC

CH2O

O

OH

OH

P

PP

CO2

CH2O

C

C

HC

CH2O

OH

OH

OH

PP

P

CH2O

C

C

HC

CH2O

O

OH

C OHO

-OC

O

OOH

H

CH2O

C

C

OH

O

O-

P

2

Reactions of the dark process

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.

Structure of the ribulose 1,5 diphosphate carboxylase

Journal of Molecular Biology 2002, 316, 679

Active centre of the ribulose 1,5-diphosphate carboxylase enzyme of C. Reinhardtii green algae in the presence of a model substrate.

Active centre of the ribulose 1,5-diphosphate carboxylase

Journal of Molecular Biology 2002, 316, 679

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

Photosynthesis

Evolution of photosynthesis

Reaction centre of the purple bacteria

Green sulphur bacteria:

The photosynthesis

Artificial photosynthesis

Coordination Chemistry Reviews 252 (2008) 444

Artificial photosynthesis

Coordination Chemistry Reviews 252 (2008) 456

Artificial photosynthesis

Photosynthetic car?