Metabolic Modeling Tutorial
discounted EARLY registration ends Dec 31, 2014
BioCyc websites down
12/28 - 12/31
for maintenance.
Metabolic Modeling Tutorial
discounted EARLY registration ends Dec 31, 2014
BioCyc websites down
12/28 - 12/31
for maintenance.
Metabolic Modeling Tutorial
discounted EARLY registration ends Dec 31, 2014
BioCyc websites down
12/28 - 12/31
for maintenance.
Metabolic Modeling Tutorial
discounted EARLY registration ends Dec 31, 2014
BioCyc websites down
12/28 - 12/31
for maintenance.
Metabolic Modeling Tutorial
discounted EARLY registration ends Dec 31, 2014
BioCyc websites down
12/28 - 12/31
for maintenance.
twitter

MetaCyc Enzyme: photosystem I

Synonyms: PS I, photosystem I trimer

Species: Synechococcus elongatus PCC 7942

Subunit composition of photosystem I = [([PsaA][PsaB])(PsaC)(PsaD)(PsaE)(PsaF)(PsaI)(PsaJ)(PsaK)(PsaL)]3
         photosystem I monomer = ([PsaA][PsaB])(PsaC)(PsaD)(PsaE)(PsaF)(PsaI)(PsaJ)(PsaK)(PsaL)
                 photosystem I core protein = (PsaA)(PsaB) (summary available)
                 PSI-C = PsaC (summary available)

Summary:
Photosystem I (PS I) is a large membrane protein complex that catalyzes the light driven electron transfer from plastocyanin, which is located on the inside of the thylakoids (the lumen), to ferredoxin, which is on the stromal side of the membrane.

Cyanobacterial PS I can exist in both trimeric and monomeric forms. The trimeric form has been shown to be the prominent oligomeric state at low light intensity. The monomeric unit of PSI from Synechococcus elongatus consists of 10 protein subunits, to which 127 cofactors are non-covalently bound. The 10 proteins are PsaA, PsaB, PSI-C, PsaD, PsaE, PsaF, PsaI, PsaJ, PsaK, PsaL. Other cyanobacteria may contain two additional subunits - PsaM and PsaX. PsaM is unique to some cyanobacteria, and has not been identified in Synechococcus elongatus PCC 7942, while PsaX is only found in thermophilic cyanobacteria.

The processes catalyzed by Photosystem I can be divided into:

1. light capturing and excitation energy transfer

2. electron transfer.

The light capturing is performed by the large antenna system that consists of 90 antenna chlorophylls and 22 carotenoids. The excitation energy is transferred to the center of the complex, where the electron transport chain is located. The electron transport chain consists of six chlorophylls, two phylloquinones and three 4Fe4S clusters.

The charge separation is initiated from P700, the electron donor, which consists of a heterodimer of a chlorophyll a and a chlorophyll a' (the C13 epimer of chlorophyll a). From P700, the electron is transferred stepwise to A (a chlorophyll a molecule), A0 (also a chlorophyll a molecule), A1 (a phylloquinone molecule) and from there subsequently to the three a [4Fe-4S] iron-sulfur cluster, named FX, FA and FB. After the docking of ferredoxin, the electron is transferred from the terminal 4Fe4S cluster of PS I, FB, to the 2Fe2S cluster of ferredoxin, which transfers the electron to the ferredoxin-NADP oxidoreductase, where NADP+ is finally reduced to NADPH. Under conditions of iron limitation, a flavodoxin may replace the ferredoxin [Grotjohann05].

P700 is re-reduced with the electrons delivered from PS II by plastocyanin.

Gene-Reaction Schematic: ?

Credits:
Created 19-May-2008 by Caspi R , SRI International


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: ethylene biosynthesis V (engineered) , 1-butanol autotrophic biosynthesis , oxygenic photosynthesis , photosynthesis light reactions


Subunit of photosystem I: photosystem I monomer


Subunit of photosystem I monomer: photosystem I core protein

Synonyms: P700 protein

Summary:
The large subunits PsaA and PsaB are the most important subunits of photosystem I, located in the center of the photosystem I monomer. They harbor the majority of chlorophylls and carotenoids of the antenna system as well as most of the cofactors of the electron transport chain from P700 to the first FeS cluster, FX.


Subunit of photosystem I core protein: PsaA

Synonyms: Photosystem I P700 chlorophyll a apoprotein A1

Gene: psaA Accession Number: SYNPCC7942_2049 (MetaCyc)

Locations: thylakoid membrane

Sequence Length: 763 AAs

Molecular Weight: 83.905 kD (from nucleotide sequence)

GO Terms:

Cellular Component: GO:0042651 - thylakoid membrane

Gene Class: UNCLASSIFIED

Unification Links: KEGG:Synpcc7942_2049 , Protein Model Portal:Q31LJ0 , SMR:Q31LJ0 , String:1140.Synpcc7942_2049 , UniProt:Q31LJ0

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:
PsaA together with PsaB form a heterodimer which comprises the central core of Photosystem I. 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 core protein: PsaB

Synonyms: Photosystem I P700 chlorophyll a apoprotein A2

Gene: psaB Accession Number: SYNPCC7942_2048 (MetaCyc)

Locations: thylakoid membrane

Sequence Length: 734 AAs

Molecular Weight: 81.476 kD (from nucleotide sequence)

GO Terms:

Cellular Component: GO:0042651 - thylakoid membrane

Gene Class: UNCLASSIFIED

Unification Links: KEGG:Synpcc7942_2048 , Protein Model Portal:Q31LJ1 , SMR:Q31LJ1 , String:1140.Synpcc7942_2048 , UniProt:Q31LJ1

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:
The plastocyanin/cytochrome c6-ferredoxin oxidoreductase Photosystem I converts photonic excitation into a charge separation. This enables the transfer of an electron from the electron donor P700 to the electron acceptors A0, A1, FX, FA and FB in turn. Plastocyanin or cytochrome c6 reduces the oxidized P700 on the lumenal side of the thylakoid membrane.

The subunits PsaA and PsaB binds to the electron donor P700 at the reaction center, the heart of PSI [Scheller01]. The PsA/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 monomer: PSI-C

Synonyms: PsaC, Photosystem I iron-sulfur center

Gene: psaC Accession Number: SYNPCC7942_0535 (MetaCyc)

Locations: thylakoid membrane

Sequence Length: 81 AAs

Molecular Weight: 8.798 kD (from nucleotide sequence)

GO Terms:

Cellular Component: GO:0042651 - thylakoid membrane

Gene Class: UNCLASSIFIED

Unification Links: KEGG:Synpcc7942_0535 , Pride:Q31QV2 , Protein Model Portal:Q31QV2 , SMR:Q31QV2 , String:1140.Synpcc7942_0535 , UniProt:Q31QV2

Relationship Links: InterPro:IN-FAMILY:IPR001450 , 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:
The subunits PSI-C, PSI-D and PSI-E are extrinsic subunits that form a stromal hump, which extends beyond the membrane by 90 Å. All three subunits together form the docking site for ferredoxin. PSI-C is the most important of the three extrinsic subunits, since it carries the two terminal a [4Fe-4S] iron-sulfur cluster, FA and FB.


Subunit of photosystem I monomer: PsaD

Synonyms: photosystem I reaction center subunit II

Gene: psaD Accession Number: SYNPCC7942_1002 (MetaCyc)

Locations: thylakoid membrane

Sequence Length: 142 AAs

Molecular Weight: 15.646 kD (from nucleotide sequence)

GO Terms:

Cellular Component: GO:0042651 - thylakoid membrane

Gene Class: UNCLASSIFIED

Unification Links: KEGG:Synpcc7942_1002 , Protein Model Portal:Q31PI7 , SMR:Q31PI7 , String:1140.Synpcc7942_1002 , UniProt:Q31PI7

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

Summary:
PsaD is an extrinsic subunit which forms part of the docking site for ferredoxin [Lagoutte01]. It is essential for the electron transfer from PSI to ferredoxin and allows PSI-C to adjust its final position in the complex. PsaD requires the presence of the PsaL subunit for stabilization in cyanobacteria [Grotjohann05].


Subunit of photosystem I monomer: PsaE

Synonyms: Photosystem I reaction center subunit IV

Gene: psaE Accession Number: SYNPCC7942_1322 (MetaCyc)

Sequence Length: 75 AAs

Molecular Weight: 8.138 kD (from nucleotide sequence)

Gene Class: UNCLASSIFIED

Unification Links: KEGG:Synpcc7942_1322 , Protein Model Portal:Q31NL7 , SMR:Q31NL7 , String:1140.Synpcc7942_1322 , UniProt:Q31NL7

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

Summary:
PsaE is an extrinsic subunit and contributes to the docking site for ferredoxin. When PsaE is deleted in cells, they compensate by increasing the level of ferredoxin [Golbeck06]. It has been suggested that PsaE may play a role in cyclic electron transport [Thomas01].


Subunit of photosystem I monomer: PsaF

Synonyms: photosystem I reaction center subunit III precursor

Gene: psaF Accession Number: SYNPCC7942_1250 (MetaCyc)

Locations: thylakoid membrane

Sequence Length: 159 AAs

Molecular Weight: 17.109 kD (from nucleotide sequence)

GO Terms:

Cellular Component: GO:0042651 - thylakoid membrane

Gene Class: UNCLASSIFIED

Unification Links: KEGG:Synpcc7942_1250 , Protein Model Portal:Q31NT9 , SMR:Q31NT9 , String:1140.Synpcc7942_1250 , UniProt:Q31NT9

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

Summary:
PsaF has hydrophobic interactions with chlorophylls an carotenoids [Grotjohann05]. Two roles have been proposed for PsaF: shielding of the carotenoids and of chlorophylls of the antenna from the lipid phase, and mediation of the excitation energy transfer from the external antenna system (i.e., IsiA chlorophyll-binding protein and the phycobilisomes) to the PS I core [Grotjohann05].


Subunit of photosystem I monomer: PsaI

Synonyms: Photosystem I PsaI protein, Photosystem I subunit VIII

Gene: psaI Accession Number: SYNPCC7942_2343 (MetaCyc)

Locations: thylakoid membrane

Sequence Length: 38 AAs

Molecular Weight: 4.003 kD (from nucleotide sequence)

GO Terms:

Cellular Component: GO:0042651 - thylakoid membrane

Gene Class: UNCLASSIFIED

Unification Links: KEGG:Synpcc7942_2343 , Protein Model Portal:P95823 , SMR:P95823 , String:P95823 , UniProt:P95823

Relationship Links: InterPro:IN-FAMILY:IPR001302 , Pfam:IN-FAMILY:PF00796

Summary:
PsaI is one of the smaller subunits of PSI and forms contacts with PsaL and PsaM [Grotjohann05].


Subunit of photosystem I monomer: PsaJ

Synonyms: photosystem I reactionCenter subunit IX

Gene: psaJ Accession Number: SYNPCC7942_1249 (MetaCyc)

Locations: thylakoid membrane

Sequence Length: 44 AAs

Molecular Weight: 5.025 kD (from nucleotide sequence)

GO Terms:

Cellular Component: GO:0042651 - thylakoid membrane

Gene Class: UNCLASSIFIED

Unification Links: KEGG:Synpcc7942_1249 , Protein Model Portal:Q31NU0 , SMR:Q31NU0 , String:1140.Synpcc7942_1249 , UniProt:Q31NU0

Relationship Links: InterPro:IN-FAMILY:IPR002615 , Pfam:IN-FAMILY:PF01701 , ProDom:IN-FAMILY:PD004198

Summary:
This protein binds two chlorophyll-a molecules and enables the organization of the psaE and psaF subunits and is required for efficient PSI excitation [Schottler07]. It is located at the outer boundary of PSI, in proximity to the docking sites for Lhca2 and Lhca3 and the binding site for plastocyanin [Schottler07].


Subunit of photosystem I monomer: PsaK

Synonyms: Photosystem I reaction center subunit PsaK 1

Gene: psaK Accession Number: SYNPCC7942_0407 (MetaCyc)

Locations: thylakoid membrane

Sequence Length: 80 AAs

Molecular Weight: 8.179 kD (from nucleotide sequence)

GO Terms:

Cellular Component: GO:0042651 - thylakoid membrane

Gene Class: UNCLASSIFIED

Unification Links: KEGG:Synpcc7942_0407 , Protein Model Portal:Q31R80 , SMR:Q31R80 , String:1140.Synpcc7942_0407 , UniProt:Q31R80

Relationship Links: InterPro:IN-FAMILY:IPR000549 , InterPro:IN-FAMILY:IPR017492 , 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].


Subunit of photosystem I monomer: PsaL

Synonyms: photosystem I reaction center subunit XI, PSI subunit V, PSI-L

Gene: psaL Accession Number: SYNPCC7942_2342 (MetaCyc)

Locations: thylakoid membrane

Sequence Length: 166 AAs

Molecular Weight: 17.293 kD (from nucleotide sequence)

GO Terms:

Cellular Component: GO:0042651 - thylakoid membrane

Unification Links: KEGG:Synpcc7942_2342 , Protein Model Portal:P95822 , String:1140.Synpcc7942_2342 , UniProt:P95822

Relationship Links: InterPro:IN-FAMILY:IPR003757 , InterPro:IN-FAMILY:IPR022980 , Pfam:IN-FAMILY:PF02605 , ProDom:IN-FAMILY:PD005947

Summary:
PsaL has hydrophobic interaction with other carotenoids and coordinates three antenna chlorophyll-a [Grotjohann05]. It mediates much of the contact between monomers in the trimerization domain [Grotjohann05].


References

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

Lagoutte01: Lagoutte B, Hanley J, Bottin H (2001). "Multiple functions for the C terminus of the PsaD subunit in the cyanobacterial photosystem I complex." Plant Physiol 126(1);307-16. PMID: 11351094

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

Park06: Park YJ, Yoo CB, Choi SY, Lee HB (2006). "Purifications and characterizations of a ferredoxin and its related 2-oxoacid:ferredoxin oxidoreductase from the hyperthermophilic archaeon, Sulfolobus solfataricus P1." J Biochem Mol Biol 39(1);46-54. PMID: 16466637

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

Schottler07: Schottler MA, Flugel C, Thiele W, Stegemann S, Bock R (2007). "The plastome-encoded PsaJ subunit is required for efficient Photosystem I excitation, but not for plastocyanin oxidation in tobacco." Biochem J 403(2);251-60. PMID: 17209805

Thomas01: Thomas DJ, Thomas J, Youderian PA, Herbert SK (2001). "Photoinhibition and light-induced cyclic electron transport in ndhB(-) and psaE(-) mutants of Synechocystis sp. PCC 6803." Plant Cell Physiol 42(8);803-12. PMID: 11522905


Report Errors or Provide Feedback
Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
Page generated by SRI International Pathway Tools version 18.5 on Sun Dec 21, 2014, biocyc14.