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MetaCyc Enzyme: photosystem I

Synonyms: PSI

Species: Arabidopsis thaliana col

Subunit composition of photosystem I = [PsaO][PsaG][PsaK][PsaF][PsaH1][PsaL][PsaN][PsaE2][PsaC][PsaD1][PsaA][PsaB]
         Photosystem I subunit O = PsaO (summary available)
         Photosystem I reaction center subunit V = PsaG (summary available)
         Photosystem I reaction center subunit psaK = PsaK (summary available)
         Photosystem I reaction center subunit III = PsaF (summary available)
         Photosystem I reaction center subunit VI-1 = PsaH1 (summary available)
         Photosystem I reaction center subunit XI = PsaL (summary available)
         Photosystem I reaction center subunit N = PsaN (summary available)
         Photosystem I reaction center subunit IV B = PsaE2 (summary available)
         Photosystem I iron-sulfur center = PsaC (summary available)
         Photosystem I reaction center subunit II-1 = PsaD1 (summary available)
         Photosystem I P700 chlorophyll a apoprotein A1 = PsaA (summary available)
         Photosystem I P700 chlorophyll a apoprotein A2 = PsaB (summary available)

Summary:
The function of PSI is to produce the NADPH necessary for the reduction of CO2 in the Calvin-Benson-Bassham cycle.

PSI is a multiprotein complex of up to 15 core subunits and is trimeric in cyanobacteria [Ozawa10]. In algae and higher plants the PSI core is associated with the peripheral light-harvesting antenna complex I (LHCI) that together form the PSI-LHCI supercomplex [Ozawa10]. PSI is associated with cofactors, such as chlorophyll, a, β carotene, lipid and iron sulfur clusters [Wicke11]. PSI uses solar energy to generate P700 [Webber01]. P700 is the primary electron donor that catalyzes electron transfer from plastocyanin or cytochrome c6 to the intermediate electron acceptors A0, A1 and FX [Sun99]. This culminates in the transfer of an electron to NADP+ to form NADPH via ferredoxin and the associated oxidoreductase.

P700 is a dimer of chlorophyll a and a' stabilized by PsaA and PsaB [Vassiliev95]. This forms the reaction center (RC) at the core of PSI. PsaF and PsaN are involved in docking plastocyanin or cytochrome c6 to the PSI complex and for efficient electron transfer to P700+ [Hippler97]. Two 4[FeS] clusters (FA and FB), the terminal electron acceptors bind to peripheral subunit PsaC, which together with PsaD and PsaE forms the docking site for ferredoxin to the PSI complex on the stromal side [Ozawa10].

PsaG, PsaH, and PsaN are special to eukaryotes and are involved in binding the light harvesting polypeptides. Some newly characterized accessory proteins Inner membrane ALBINO3-like protein 1 and Inner membrane ALBINO3-like protein 2 are crucial in mediating LHC protein integration into the thylakoid membrane [Gohre06].

Chaperone proteins that play a pivotal role in the stepwise integration of PSI subunits into a functional complex have recently been elucidated. These include chloroplast encoded Ycf4 and Ycf3, located in the thylakoid membrane that are required for a posttranslational step of PSI assembly [Albus10].

Citations: [Melkozernov06, Jensen00]

Locations: chloroplast thylakoid

Gene-Reaction Schematic: ?

GO Terms:

Cellular Component: GO:0009534 - chloroplast thylakoid

Credits:
Revised 05-May-2011 by Weerasinghe D


Enzymatic reaction of: photosystem I

EC Number: 1.97.1.12

a reduced plastocyanin + an oxidized ferredoxin + hν <=> an oxidized plastocyanin + a reduced ferredoxin

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the Enzyme Commission system.

The reaction is favored in the direction shown.

In Pathways: photosynthesis light reactions


Subunit of photosystem I: Photosystem I subunit O

Synonyms: Putative 16kDa membrane protein

Gene: PsaO Accession Number: AT1G08380 (MetaCyc)

Locations: plastid

Molecular Weight: 15.14 kD (from nucleotide sequence)

GO Terms:

Cellular Component: GO:0009536 - plastid

Unification Links: KEGG:AT1G08380 , PhylomeDB:Q949Q5 , Pride:Q949Q5 , String:Q949Q5 , UniProt:Q949Q5

Relationship Links: InterPro:IN-FAMILY:IPR017498

Summary:
PsaO forms a domain in PSI that is involved in the interaction with light-harvesting complex II and mediates the balance of excitation energy between the two photosystems [Jensen04].

Citations: [Knoetzel02]


Subunit of photosystem I: Photosystem I reaction center subunit V

Synonyms: PSI-G

Gene: PsaG Accession Number: AT1G55670 (MetaCyc)

Locations: chloroplast

Molecular Weight: 17.08 kD (from nucleotide sequence)

GO Terms:

Cellular Component: GO:0009507 - chloroplast

Unification Links: KEGG:K08905 , PhylomeDB:Q9S7N7 , Pride:Q9S7N7 , Protein Model Portal:Q9S7N7 , SMR:Q9S7N7 , String:Q9S7N7 , UniProt:Q9S7N7

Relationship Links: InterPro:IN-FAMILY:IPR000549 , InterPro:IN-FAMILY:IPR016370 , InterPro:IN-FAMILY:IPR017494 , InterPro:IN-FAMILY:IPR023618 , Pfam:IN-FAMILY:PF01241 , Prosite:IN-FAMILY:PS01026

Summary:
PSI-G is a subunit of photosystem I and is present in eukaryotes [Jensen02]. It is an integral membrane protein and together with PSI-K comprise the LHCI-binding proteins [Scheller01]. PSI-G is involved in binding to LHCI-680 and in the interaction between LHCI and the PSI core. It also plays a role in stabilizing the binding of the peripheral antenna and regulation of PSI [Moller05].


Subunit of photosystem I: Photosystem I reaction center subunit psaK

Synonyms: PSI-K, Photosystem I subunit X

Gene: PsaK Accession Number: G-663 (MetaCyc)

Locations: chloroplast

Molecular Weight: 13.2 kD (from nucleotide sequence)

GO Terms:

Cellular Component: GO:0009507 - chloroplast

Unification Links: KEGG:AT1G30380 , PhylomeDB:Q9SUI5 , Pride:Q9SUI5 , Protein Model Portal:Q9SUI5 , SMR:Q9SUI5 , String:Q9SUI5 , UniProt:Q9SUI5

Relationship Links: InterPro:IN-FAMILY:IPR000549 , InterPro:IN-FAMILY:IPR016370 , InterPro:IN-FAMILY:IPR017493 , InterPro:IN-FAMILY:IPR023618 , Pfam:IN-FAMILY:PF01241 , Prosite:IN-FAMILY:PS01026

Summary:
PsaK is located at the periphery of the PSI complex and contacts the membrane bilayer. It may be involved in the interaction of PSI with its external antenna system LHCI in higher plants [Ozawa10]. The protein coordinates two chlorophylls and interacts with carotenoids [Golbeck06].

Citations: [Jensen00, Scheller01]


Subunit of photosystem I: Photosystem I reaction center subunit III

Synonyms: PSI-F

Gene: PsaF Accession Number: G-664 (MetaCyc)

Locations: chloroplast

Molecular Weight: 24.17 kD (from nucleotide sequence)

GO Terms:

Cellular Component: GO:0009507 - chloroplast

Unification Links: KEGG:AT1G31330 , PhylomeDB:Q9SHE8 , Pride:Q9SHE8 , Protein Model Portal:Q9SHE8 , SMR:Q9SHE8 , String:3702.AT1G31330.1-P , UniProt:Q9SHE8

Relationship Links: InterPro:IN-FAMILY:IPR003666 , Pfam:IN-FAMILY:PF02507

Summary:
PSI-F is an integral membrane protein involved in the docking of plastocyanin to PSI [Haldrup00]. Plants lacking PSI-F are hampered in energy transfer from LHCI and have a reduced rate of electron donation from plastocyanin to P700 [Hippler97]. In the absence of PSI-F, Lhca1 and Lhca4 cannot transfer energy from LHCI to the reaction center [Scheller01].


Subunit of photosystem I: Photosystem I reaction center subunit VI-1

Synonyms: PSI-H1

Gene: PsaH1 Accession Number: G-665 (MetaCyc)

Locations: chloroplast

Molecular Weight: 15.21 kD (from nucleotide sequence)

GO Terms:

Cellular Component: GO:0009507 - chloroplast

Unification Links: KEGG:AT3G16140 , PhylomeDB:Q9SUI7 , Pride:Q9SUI7 , Protein Model Portal:Q9SUI7 , SMR:Q9SUI7 , String:Q9SUI7 , UniProt:Q9SUI7

Relationship Links: InterPro:IN-FAMILY:IPR004928 , Pfam:IN-FAMILY:PF03244

Summary:
PSI-H1 is essential for state transitions in photosynthesis, and is possibly involved in docking of the LHC I antenna complex to the core complex [Haldrup06].

Citations: [Naver99, Lunde00]


Subunit of photosystem I: Photosystem I reaction center subunit XI

Synonyms: PSI subunit V, PSI-L

Gene: PsaL Accession Number: G-666 (MetaCyc)

Locations: chloroplast

Molecular Weight: 23.05 kD (from nucleotide sequence)

GO Terms:

Cellular Component: GO:0009507 - chloroplast

Unification Links: KEGG:AT4G12800 , PhylomeDB:Q9SUI4 , Pride:Q9SUI4 , Protein Model Portal:Q9SUI4 , SMR:Q9SUI4 , String:Q9SUI4 , UniProt:Q9SUI4

Relationship Links: InterPro:IN-FAMILY:IPR003757 , PDB:Structure:1YO9 , Pfam:IN-FAMILY:PF02605 , ProDom:IN-FAMILY:PD005947

Summary:
PSI-L is involved stabilisation of PSI-H in eukaryotes. In transgenic plants when PSI-L is downregulated, there is a secondary loss of PSI-H [Ihalainen02].


Subunit of photosystem I: Photosystem I reaction center subunit N

Synonyms: PSI-N

Gene: PsaN Accession Number: G-667 (MetaCyc)

Locations: chloroplast

Molecular Weight: 18.42 kD (from nucleotide sequence)

GO Terms:

Cellular Component: GO:0009507 - chloroplast

Unification Links: KEGG:AT5G64040

Relationship Links: UniProt:PART-OF:P49107

Summary:
PSI-N is the only subunit found completely on the lumenal side of PSI [Nielsen94]. It may function in mediating the binding of the antenna complexes to the PSI reaction center and core antenna. It does not bind pigments and plays an important role in docking plastocyanin to the PSI complex [Ihalainen02].

Citations: [Haldrup99, Scheller01]


Subunit of photosystem I: Photosystem I reaction center subunit IV B

Gene: psaE2 Accession Number: G-668 (MetaCyc)

Locations: chloroplast

Molecular Weight: 15.18 kD (from nucleotide sequence)

GO Terms:

Cellular Component: GO:0009507 - chloroplast

Unification Links: KEGG:AT2G20260 , PhylomeDB:Q9S714 , Pride:Q9S714 , Protein Model Portal:Q9S714 , SMR:Q9S714 , String:Q9S714 , UniProt:Q9S714

Relationship Links: InterPro:IN-FAMILY:IPR003375 , InterPro:IN-FAMILY:IPR008990 , Pfam:IN-FAMILY:PF02427 , ProDom:IN-FAMILY:PD004772

Summary:
Hydrophilic stromal PSI-E stabilizes the interaction between psaC and the PSI core, assists in the docking of ferredoxin to PSI and interacts with ferredoxin-NADP oxidoreductase. PSI-E is required for optimal electron transport to ferredoxin and flavodoxin [Rousseau93].

Citations: [Varotto00, vanThor99]


Subunit of photosystem I: Photosystem I iron-sulfur center

Synonyms: FrxA, PsaC, PSI-C, Photosystem I subunit VII

Gene: psaC Accession Number: G-669 (MetaCyc)

Locations: chloroplast

Molecular Weight: 9.03 kD (from nucleotide sequence)

GO Terms:

Cellular Component: GO:0009507 - chloroplast

Unification Links: KEGG:ArthCp075 , Pride:P62090 , Protein Model Portal:P62090 , SMR:P62090 , String:3702.ATCG01060.1-P , UniProt:P62090

Relationship Links: InterPro:IN-FAMILY:IPR017491 , InterPro:IN-FAMILY:IPR017896 , InterPro:IN-FAMILY:IPR017900 , Pfam:IN-FAMILY:PF12838 , Prosite:IN-FAMILY:PS00198 , Prosite:IN-FAMILY:PS51379

Summary:
Stromal PsaC is a 2[4Fe-4S] component of photosystem I (PSI) which binds the electron acceptors FA and FB [Fischer98]. The terminal electron acceptor of PSI, FB donates electrons to ferredoxin. The isolated PSI-C holoprotein lacks stability in the presence of oxygen [Scheller01].


Subunit of photosystem I: Photosystem I reaction center subunit II-1

Synonyms: Photosystem I 20 kDa subunit 1, PSI-D1

Gene: psaD1 Accession Number: G-670 (MetaCyc)

Locations: chloroplast

Molecular Weight: 22.59 kD (from nucleotide sequence)

GO Terms:

Cellular Component: GO:0009507 - chloroplast

Unification Links: KEGG:AT4G02770 , Mint:MINT-8199695 , PhylomeDB:Q9S7H1 , Pride:Q9S7H1 , Protein Model Portal:Q9S7H1 , SMR:Q9S7H1 , String:Q9S7H1 , UniProt:Q9S7H1

Relationship Links: InterPro:IN-FAMILY:IPR003685 , Pfam:IN-FAMILY:PF02531

Summary:
PSI-D interacts strongly with and plays an important function in the docking of ferredoxin. PSI-D binds tightly to PSI-C in plant PSI [Scheller01].


Subunit of photosystem I: Photosystem I P700 chlorophyll a apoprotein A1

Synonyms: PsaA, PSI-A

Gene: psaA Accession Number: G-671 (MetaCyc)

Locations: chloroplast

Molecular Weight: 83.23 kD (from nucleotide sequence)

GO Terms:

Cellular Component: GO:0009507 - chloroplast

Unification Links: KEGG:ArthCp022 , Pride:P56766 , Protein Model Portal:P56766 , SMR:P56766 , String:3702.ATCG00350.1-P , UniProt:P56766

Relationship Links: InterPro:IN-FAMILY:IPR001280 , InterPro:IN-FAMILY:IPR006243 , InterPro:IN-FAMILY:IPR020586 , Pfam:IN-FAMILY:PF00223 , Prints:IN-FAMILY:PR00257 , Prosite:IN-FAMILY:PS00419

Summary:
PSI consists of a core complex that captures photons, and an electron transfer chain that converts photon excitation into a charge separation. This transfers an electron from the donor P700 to the acceptors A0, A1, FX, FA and FB in turn.

The subunits PSI-A and PSI-B binds to P700 at the reaction center, the heart of PSI [Scheller01]. The PSI-A/B heterodimer can be isolated as a complex known as chlorophyll a-complex 1 (CP1) and contains most of the pigments of PSI [Scheller01].


Subunit of photosystem I: Photosystem I P700 chlorophyll a apoprotein A2

Synonyms: PsaB, PSI-B

Gene: psaB Accession Number: G-672 (MetaCyc)

Locations: chloroplast

Molecular Weight: 82.47 kD (from nucleotide sequence)

GO Terms:

Cellular Component: GO:0009507 - chloroplast

Unification Links: KEGG:ArthCp021 , Pride:P56767 , Protein Model Portal:P56767 , SMR:P56767 , String:3702.ATCG00340.1-P , UniProt:P56767

Relationship Links: InterPro:IN-FAMILY:IPR001280 , InterPro:IN-FAMILY:IPR006244 , InterPro:IN-FAMILY:IPR020586 , Pfam:IN-FAMILY:PF00223 , Prints:IN-FAMILY:PR00257 , Prosite:IN-FAMILY:PS00419

Summary:
PSI consists of a core complex that captures photons, and an electron transfer chain that converts photon excitation into a charge separation. This transfers an electron from the donor P700 to the acceptors A0, A1, FX, FA and FB in turn.

The subunits PSI-A and PSI-B binds to P700 at the reaction center, the heart of PSI [Scheller01]. The PSI-A/B heterodimer can be isolated as a complex known as chlorophyll a-complex 1 (CP1) and contains most of the pigments of PSI [Scheller01].


References

Albus10: Albus CA, Ruf S, Schottler MA, Lein W, Kehr J, Bock R (2010). "Y3IP1, a nucleus-encoded thylakoid protein, cooperates with the plastid-encoded Ycf3 protein in photosystem I assembly of tobacco and Arabidopsis." Plant Cell 22(8);2838-55. PMID: 20807881

Fischer98: Fischer N, Hippler M, Setif P, Jacquot JP, Rochaix JD (1998). "The PsaC subunit of photosystem I provides an essential lysine residue for fast electron transfer to ferredoxin." EMBO J 17(4);849-58. PMID: 9463363

Gohre06: Gohre V, Ossenbuhl F, Crevecoeur M, Eichacker LA, Rochaix JD (2006). "One of two alb3 proteins is essential for the assembly of the photosystems and for cell survival in Chlamydomonas." Plant Cell 18(6);1454-66. PMID: 16679460

Golbeck06: Golbeck J. H. (2006). "Photosystem I The Light Driven Plastocyanin:Ferredoxin Oxidoreductase." Advances in Photosynthesis and Respiration.

Grotjohann05: Grotjohann I, Fromme P (2005). "Structure of cyanobacterial photosystem I." Photosynth Res 85(1);51-72. PMID: 15977059

Haldrup00: Haldrup A, Simpson DJ, Scheller HV (2000). "Down-regulation of the PSI-F subunit of photosystem I (PSI) in Arabidopsis thaliana. The PSI-F subunit is essential for photoautotrophic growth and contributes to antenna function." J Biol Chem 2000;275(40);31211-8. PMID: 10900198

Haldrup06: Haldrup A, Jensen P. E., Scheller H. V. (2006). "The Low Molecular Mass Subunits in Higher Plant Photosystem I." Advances in Photosynthesis and Respiration.

Haldrup99: Haldrup A, Naver H, Scheller HV (1999). "The interaction between plastocyanin and photosystem I is inefficient in transgenic Arabidopsis plants lacking the PSI-N subunit of photosystem I." Plant J 1999;17(6);689-98. PMID: 10230065

Hippler97: Hippler M, Drepper F, Farah J, Rochaix JD (1997). "Fast electron transfer from cytochrome c6 and plastocyanin to photosystem I of Chlamydomonas reinhardtii requires PsaF." Biochemistry 36(21);6343-9. PMID: 9174349

Ihalainen02: Ihalainen JA, Jensen PE, Haldrup A, van Stokkum IH, van Grondelle R, Scheller HV, Dekker JP (2002). "Pigment organization and energy transfer dynamics in isolated photosystem I (PSI) complexes from Arabidopsis thaliana depleted of the PSI-G, PSI-K, PSI-L, or PSI-N subunit." Biophys J 83(4);2190-201. PMID: 12324436

Jensen00: Jensen PE, Gilpin M, Knoetzel J, Scheller HV (2000). "The PSI-K subunit of photosystem I is involved in the interaction between light-harvesting complex I and the photosystem I reaction center core." J Biol Chem 2000;275(32);24701-8. PMID: 10818090

Jensen02: Jensen PE, Rosgaard L, Knoetzel J, Scheller HV (2002). "Photosystem I activity is increased in the absence of the PSI-G subunit." J Biol Chem 2002;277(4);2798-803. PMID: 11707465

Jensen04: Jensen PE, Haldrup A, Zhang S, Scheller HV (2004). "The PSI-O subunit of plant photosystem I is involved in balancing the excitation pressure between the two photosystems." J Biol Chem 279(23);24212-7. PMID: 15169790

Knoetzel02: Knoetzel J, Mant A, Haldrup A, Jensen PE, Scheller HV (2002). "PSI-O, a new 10-kDa subunit of eukaryotic photosystem I." FEBS Lett 2002;510(3);145-8. PMID: 11801243

Lunde00: Lunde C, Jensen PE, Haldrup A, Knoetzel J, Scheller HV (2000). "The PSI-H subunit of photosystem I is essential for state transitions in plant photosynthesis." Nature 408(6812);613-5. PMID: 11117752

Melkozernov06: Melkozernov AN, Barber J, Blankenship RE (2006). "Light harvesting in photosystem I supercomplexes." Biochemistry 45(2);331-45. PMID: 16401064

Moller05: Moller S. G. (2005). "Plastids."

Naver99: Naver H, Haldrup A, Scheller HV (1999). "Cosuppression of photosystem I subunit PSI-H in Arabidopsis thaliana. Efficient electron transfer and stability of photosystem I is dependent upon the PSI-H subunit." J Biol Chem 1999;274(16);10784-9. PMID: 10196152

Nielsen94: Nielsen VS, Mant A, Knoetzel J, Moller BL, Robinson C (1994). "Import of barley photosystem I subunit N into the thylakoid lumen is mediated by a bipartite presequence lacking an intermediate processing site. Role of the delta pH in translocation across the thylakoid membrane." J Biol Chem 269(5);3762-6. PMID: 8106420

Ozawa10: Ozawa S, Onishi T, Takahashi Y (2010). "Identification and characterization of an assembly intermediate subcomplex of photosystem I in the green alga Chlamydomonas reinhardtii." J Biol Chem 285(26);20072-9. PMID: 20413595

Rousseau93: Rousseau F, Setif P, Lagoutte B (1993). "Evidence for the involvement of PSI-E subunit in the reduction of ferredoxin by photosystem I." EMBO J 12(5);1755-65. PMID: 8387913

Scheller01: Scheller HV, Jensen PE, Haldrup A, Lunde C, Knoetzel J (2001). "Role of subunits in eukaryotic Photosystem I." Biochim Biophys Acta 1507(1-3);41-60. PMID: 11687207

Sun99: Sun J, Xu W, Hervas M, Navarro JA, Rosa MA, Chitnis PR (1999). "Oxidizing side of the cyanobacterial photosystem I. Evidence for interaction between the electron donor proteins and a luminal surface helix of the PsaB subunit." J Biol Chem 274(27);19048-54. PMID: 10383406

vanThor99: van Thor JJ, Geerlings TH, Matthijs HC, Hellingwerf KJ (1999). "Kinetic evidence for the PsaE-dependent transient ternary complex photosystem I/Ferredoxin/Ferredoxin:NADP(+) reductase in a cyanobacterium." Biochemistry 38(39);12735-46. PMID: 10504244

Varotto00: Varotto C, Pesaresi P, Meurer J, Oelmuller R, Steiner-Lange S, Salamini F, Leister D (2000). "Disruption of the Arabidopsis photosystem I gene psaE1 affects photosynthesis and impairs growth." Plant J 2000;22(2);115-24. PMID: 10792827

Vassiliev95: Vassiliev IR, Jung YS, Smart LB, Schulz R, McIntosh L, Golbeck JH (1995). "A mixed-ligand iron-sulfur cluster (C556SPaB or C565SPsaB) in the Fx-binding site leads to a decreased quantum efficiency of electron transfer in photosystem I." Biophys J 69(4);1544-53. PMID: 8534825

Webber01: Webber AN, Lubitz W (2001). "P700: the primary electron donor of photosystem I." Biochim Biophys Acta 1507(1-3);61-79. PMID: 11687208

Wicke11: Wicke S, Schneeweiss GM, dePamphilis CW, Muller KF, Quandt D (2011). "The evolution of the plastid chromosome in land plants: gene content, gene order, gene function." Plant Mol Biol 76(3-5);273-97. PMID: 21424877


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Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
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