1. Structure of photosystem I at atomic resolution (PS I)

2. Function of PS I

3. Genetic analysis of structure-function relations

4. Two branches in electron transport in PS I

5. PS I a photo-nano-switch

PS I is a light driven plastocyanin ferredoxin oxidoreductase.

Quantum efficiency for electron transfer is 1

PS I is part of the photosynthetic apparatus. A membrane protein chlorophyll complex one of the 4 complexes that make the transmembrane oxidoreductase system that oxidize water to O2 and reduces NADP+ to NADPH + H+, pump H+ that drive ATP synthesis.

PS I is part of the photosynthetic apparatus. A membrane protein chlorophyll complex one of the 4 complexes that make the transmembrane oxidoreductase system that oxidize water to O2 and reduces NADP+ to NADPH + H+, pump H+ that drive ATP synthesis.

Composition

12 subunits A-M, X (no H, G), 9 of them are transmembrane peptides. C, D & E are attached at the outside (storma).

M.W. 255 kDa

96 Chlorophylls, 22 carotenoids, 2 phylloquinons, 3 [4Fe4S] clusters.

Subunit arragem-ent view from stroma

FeSA/B

FeSX

Subunit C

Subunits A, B

The electron transfer chain is attached on subunits A, B & C.

P700, A0, A1, Fx, FA & FB.

P700- Chla dimer, parallel rings 3.5 A apart, perpendicular to the membrane, rings I, II partially overlap. Asymmetry: A branch has H bonds to H680 and to water. Lower spin density in the A ring of the radical P700+..

A0- Chla monomer (eC-A2, eC B2) has Mg-H-water-Asn591.

A1- phylloquinone, hydrophobic pocket LeuA722, TrpA697, TrpB673.

Two branches? QA-Fx 200ns, QB-Fx 20ns, B-branch is faster?

Fx,- 4Fe4S iron sulfur cluster, lowest potential in biology.

FA and FB- 4Fe4S iron sulfur clusters

FeSB

FeSA

FeSX

PQ

Ao (CHL)P700 (CHL2)

The electron transfer chain is attached on subunits A, B & C.

P700, A0, A1, Fx, FA & FB.

P700- Chla dimer, parallel rings 3.5 A apart, perpendicular to the membrane, rings I, II partially overlap. Asymmetry: A branch has H bonds to H680 and to water. Lower spin density in the A ring of the radical P700+..

A0- Chla monomer (eC-A2, eC B2) has Mg-H-water-Asn591.

A1- phylloquinone, hydrophobic pocket LeuA722, TrpA697, TrpB673.

Two branches? QA-Fx 200ns, QB-Fx 20ns, B-branch is faster?

Fx,- 4Fe4S iron sulfur cluster, lowest potential in biology.

FA and FB- 4Fe4S iron sulfur clusters

The electron transfer chain is attached on subunits A, B & C.

P700, A0, A1, Fx, FA & FB.

P700- Chla dimer, parallel rings 3.5 A apart, perpendicular to the membrane, rings I, II partially overlap. Asymmetry: A branch has H bonds to H680 and to water. Lower spin density in the A ring of the radical P700+..

A0- Chla monomer (eC-A2, eC B2) has Mg-H-water-Asn591.

A1- phylloquinone, hydrophobic pocket LeuA722, TrpA697, TrpB673.

Two branches? QA-Fx 200ns, QB-Fx 20ns, B-branch is faster?

Fx,- 4Fe4S iron sulfur cluster, lowest potential in biology.

FA and FB- 4Fe4S iron sulfur clusters

The electron transfer chain is attached on subunits A, B & C.

P700, A0, A1, Fx, FA & FB.

P700- Chla dimer, parallel rings 3.5 A apart, perpendicular to the membrane, rings I, II partially overlap. Asymmetry: A branch has H bonds to H680 and to water. Lower spin density in the A ring of the radical P700+..

A0- Chla monomer (eC-A2, eC B2) has Mg-H-water-Asn591.

A1- phylloquinone, hydrophobic pocket LeuA722, TrpA697, TrpB673.

Two branches? QA-Fx 200ns, QB-Fx 20ns, B-branch is faster?

Fx,- 4Fe4S iron sulfur cluster, lowest potential in biology.

FA and FB- 4Fe4S iron sulfur clusters