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

Observation of quinone oxidation (Q_o)/quinone reduction (Q_i) site interaction in the bc₁ complex via oriented EPR analysis. Jason Cooley^*,1, Fevzi Daldal¹, ¹ 415 S. University Ave, Philadelphia, PA, USA

ABSTRACT- Movement of the iron-sulfur protein (Fe-S) subunit is required for multiple turnovers to take place in the bc₁ complex, yet little is understood about what may control this mobility. Previous biochemical evidence has suggested, indirectly, that inhibition of the bc₁ low potential electron transport pathway (LPETP) affects the affinity of the mobile Fe-S subunit for the hydroquinone oxidation (Q_o) site. Taking advantage of the increased spectral resolution associated with oriented electron paramagnetic resonance (EPR) analysis of ordered membrane samples we show here that inhibition of the LPETP by inhibitors or various mutations changes the shape of the associated spectrum of the Rieske [2Fe2S] cluster. Furthermore, utilizing the hinge region suite of mutants that are deficient in the macro-movement of the Fe-S, but are still capable of discreet micro-movements at the Q_o site as a tool, we have demonstrated that blockages of individual steps of the LPETP effect the Fe-S/Q_o site interactions differently. From these differences, we propose mechanistic consequences of the abolition of individual redox-linked control points on the Fe-S/Q_o site interaction in the context of short-circuit control during bc₁ complex turnover.

KEY WORDS: b6f complex, bc1 complex, Rieske, EPR