PARENT SESSION
Posters P8A Cytochrome b-c complexes. Abstracts (382-393)

Elucidating the mechanism of superoxide production by the cytochrome bc₁ complex in Saccharomyces cervisiae. Isaac Forquer^*,1, Jonathan Cape¹, David Kramer¹, ¹ Washington State University, Pullman, WA, USA

ABSTRACT- The electron transport chain on the inner membrane of the mitochondria is a significant source of superoxide. The Cytochrome bc₁ Complex (cyt bc₁ complex) is a component of the electron transport chain that oxidizes quinol and transfers the electrons to cyt c, and is one of the sources of superoxide production (SOP). To function properly, the bc1 complex must compete with thermodynamically favorable bypass reactions, including superoxide production. We tested two hypotheses regarding the mechanism of SOP in the cyt bc₁ complex. The first hypothesis addresses whether or not the bc1 complex forms the reductant of oxygen during its normal (or non-superoxide producing) catalytic turnover. Second, we wish to determine where superoxide production takes place - in the catalytic site of the enzyme or outside, which would involve the release of some quinol oxidation intermediate. Our data show the energetic barrier for superoxide production is not distinguishable from normal Q-cycle catalysis, in which little superoxide production is detected. Also, we have eliminated cyt bL as a potential reductant for oxygen during steady state superoxide production enhanced by Antimycin A. Implications of these findings on our understanding of the Q-cycle and the formation of intermediates in the Q_o pocket will be discussed.

KEY WORDS: Cytochrome bc1 complex, superoxide production