Abstract 1924 The Possible Effects of Rieske Reduction Potential on Superoxide Formation in the bc1 Complex

The electron transport chain utilizes four protein complexes to generate an electrochemical gradient necessary for ATP synthesis. Complex III of the electron transport chain contains the Rieske protein. The [2Fe-2S] cluster of this protein is responsible for the transport of one electron during the quinol cycle (Q cycle). The successful transfer of electrons relies on an optimized reduction potential between quinol, Rieske, and cytochrome c1 to drive the electron passage. If the reduction potential of Rieske is too low, it may fail to or inefficiently accept the electron from quinol. In turn, the electron may react with molecular oxygen to produce superoxide. Superoxide is a form of reactive oxygen species (ROS) that can cause harm to the cell in large quantities. Thus, a mismatch in reduction potential between the Rieske protein and quinol may serve as a possible source of superoxide production. In order to investigate this hypothesis, two different systems are employed. The first aspect of the project focuses on measuring the reduction potential of the isolated Saccharomyces cerevisiae Rieske protein (ScRieske) in vitro. Several isolated ScRieske mutants are being produced in order to explore the effect of altering specific amino acids that are predicted to change the reduction potentials. The second part of the project centers on measuring the levels of superoxide produced by intact S. cerevisiae Complex III (ScComplex III) in vivo. The same mutants from part one are being produced in ScComplex III, and are being analyzed using growth assays to assess the phenotypic effect of the mutant and confocal microscopy to quantify the amount of superoxide produced. The Welch Foundation, Trinity Chemistry Department.