Support is requested to investigate the structure and function of photosynthetic reaction centers in photosystem 1 and the closely related green sulfur bacteria. The project will focus on the role of FeS centers and quinones as transient intermediates in electron transfer. Flash kinetic spectrophotometry and EPR spectroscopy will be used as principle analytical methods. In the case of green bacteria we will reconstitute the acceptor side with a 22 kDa FeS containing polypeptide that has been expressed in E. coli. Elucidation of the mechanism of inhibition of the quinone binding site in Photosystem 1 is important because of the potential of using this site for a new class of herbicides. A new project has been initiated on Photosystem 1 following a molecular modeling study of the core heterodimer. The lab has already tested one hypothesis generated by the modeling concerning the interaction of the subunit PsaC with the Fx domain in the core heterodimer. This will be continued together with a direct experimental test of the role of the leucine zipper motif. This will involve synthesis of peptides containing the motif and studying their physical properties. Future experiments will create models of Photosystem 1 by synthesizing designed proteins that fold into 4-.-helical bundles and installing redox centers of relevance to Photosystem 1 in the interhelical loops. This initiative will provide footholds for future studies of models that would contain photoactive components. %%% Photosynthesis is accomplished in plant and certain bacteria by the interaction of light with specialized pigment containing metal-protein complexes. The components of the complex and the ration of metal, pigment, and protein are to be analyzed in the proposal by sophisticated analytical methods. Also, the nature of the interaction of certain chemical compounds with the complex is important as a model for the design of herbicides that can interfere with photosynthesis.
