The photosystem I reaction center is reviewed from the standpoint of electron acceptors, polypeptide composition, and structural organization. Experimental difficulties in the current model are highlighted, and current results on the polypeptide location of each acceptor are reviewed. The amount of iron and labile sulfide, the types of iron-sulfur clusters, and the number of ∼ 64-kDa polypeptides are considered in light of a model for the reaction center. In particular, the presence of [2Fe-2S] clusters in photosystem I has significance in the structure and organization of Fx on the reaction center. Since four cysteinyl ligands are assumed to hold an iron-sulfur cluster, a photosystem I subunit may consist of two ∼ 64-kDa polypeptides bridged by a [2Fe-2S] cluster. The reaction center would consist of a symmetrical pair of these subunits positioned so that two [2Fe-2S] clusters are in magnetic interaction, thereby constituting Fx. The reaction center core would therefore incorporate four ∼ 64-kDa polypeptides and have a molecular weight in excess of 250 kDa.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Physical and Theoretical Chemistry
- Filtration and Separation