The photochemical reaction center complex known as Photosystem I is characterized by the presence of bound iron-sulfur centers that function as electron acceptors. Preparations of the photochemically active native Photosystem I complex contains at least one dozen subunits, most of which have no well established function. The overall objective of this project is to define the function of these subunits and to determine their structural organization. The major experimental techniques will be those of biochemical resolution and reconstitution and these methods will be supplemented with biophysical measurements to monitor the functional state of many of the electron carriers. In addition to characterizing this complex, the project will also consider the structural organization of polypeptide subunits in a reaction center complex isolated from anaerobic photosynthetic bacteria known as green sulfur bacteria since there is compelling biophysical evidence that indicates this complex has functional components that are similar to those in the plant-type Photosystem I complex. Results from this project will aid in defining the mechanism of photoinduced electron transfer in a photochemical reaction center complex and will provide information on the evolution of the photosynthetic reaction center complex from primitive to more advanced systems.
