9630413 Yu The objective of this research is to elucidate the role of subunit IV (Mr=14,384) in the cytochrome bc1 complex from a photosynthetic bacterium Rhodobacter sphaeroides. Site-directed mutagenesis, in vitro reconstitution of mutant subunit IV with the three-subunit core complex, and physical, chemical characterizations of reconstituted complex will be employed to identify (1) the tryptophan residue(s) of subunit IV essential for interaction with the three-subunit core complex; (2) the domains in subunit IV interacting with cytochrome b and with iron-sulfur protein; and (3) the amino acid residues required for stabilizing the structure of the cytochrome bc1 complex. The success of this project will increase our understanding of the structure-function and mechanism of this photosynthetic bacterial bc1 complex in particular and energy transduction in the cytochrome bc1 complex in general. A better understanding of energy transduction mechanisms in the photosynthetic apparatus will lead to increase the efficiency of photosynthesis and thus increases the renewable energy sources. %%% Photosynthesis is the process of conversion of light energy into chemical energy for use in biosynthesis. Some bacteria as well as plants have this ability. One component of the bacterial photosynthetic pathway is the cytochrome bc1 complex. Subunit IV is one component of this complex which has no obvious role in oxidation-reduction reactions. The goal of this project is to elucidate the interactions and role of this subunit within the three-subunit core complex. The experiments proposed will enhance our understanding of energy transduction mechanisms in the photosynthetic apparatus with a long-range goal of increasing the efficiency of this process. ***
