Photosynthetic Reaction Center (PSI) and Core Antenna System

from Synechococcus elongatus

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The cyanobacterial photosystem I is composed of 11 subunits, named according to their genes PsaA - F and PsaI - M. The large Subunits PsaA/B (83 kDa) are located in the thylakoid membrane, they contain the reaction center and bind about 100 molecules of chlorophyll a of the antenna system as well as ca. 20 carotinoid molecules and cofactors of the electron transfer system. PsaC (9 kDa) is extrinsic to the membrane and binds the terminal cofactors (Fe4S4 clusters). The structure of the whole complex was dissolved at a resolution of 4 Å which doesn't allow to position amino acid side chains. The model therefore is somewhat schematic. Common to the protein components (with the exception of PsaC) are long helices spanning the membrane the complex is inserted to.

Components of PSI:

PsaA/B
PsaC
PsaF/J
PsaI/L
PsaK
chlorophyll a
chlorophyll belonging to the electron transfer system
chlorophyll connecting the electron transfer system to the antenna
Fe4S4 cluster in PsaA/B
Fe4S4 cluster in PsaC

Literature:
WD Schubert et al, Photosystem I of Synechococcus elongatus at 4 Å resolution: comprehensive structure analysis, J. Mol. Biol. 272 (1997) 741-769

6-99 - R Bergmann