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Molecular Probes of Quinol Oxidation by the Cytochrome b6f complex


EMSL Project ID
2358a

Abstract

Cytochrome (cyt) b6f complex, a plastocyanin-quinol oxidoreductase, serves a central role in photosynthetic electron transport. The complex catalyzes the oxidation and reduction of quinone species at two sites on the complex: quinol oxidase (Qo) site and quinol reductase (Qi) site. The mechanism of catalysis at the Qo site is being intensely-debated, with groups supporting either one (single occupancy) or two (double occupancy) quinone species binding to the site and participating in the reaction. Several chemical inhibitors, which have been successfully used to probe these sites and deciphering the kinetic mechanism of the enzyme. We have recently produced evidence that two molecules of the quinone analog, dibromomethylisopropylbenzoquinone (DBMIB), bind simultaneously to the Qo site. DBMIB represents an excellent system in which to test and study double occupancy models. We proposed to use continuous-wave (CW) and pulsed X-band EPR techniques, to probe the nature of 'inhibitor double occupancy' in this system. The ultimate goal is to understand 1) how one and two DBMIB molecules interact with the complex; and 2) how they are oriented within the Qo binding pocket. The facilities at EMSL, including especially the expertise of Dr. M. Bowman, are ideally suited for this work. This would require approximately 280 hours of time on the X-band EPR spectrometer that is available at EMSL.

Project Details

Project type
Capability Research
Start Date
2005-02-15
End Date
2006-12-28
Status
Closed

Team

Principal Investigator

David Kramer
Institution
Washington State University

Team Members

Michael Bowman
Institution
University of Alabama

Jonathan Cape
Institution
Washington State University

Isaac Forquer
Institution
Washington State University

Related Publications

Cape JL, JR Strahan, MJ Lenaeus, BA Yuknis, TT Le, J Shepherd, MK Bowman, and DM Kramer. 2005. "THE RESPIRATORY SUBSTRATE RHODOQUINOL INDUCES Q-CYCLE BYPASS REACTIONS IN THE YEAST CYTOCHROME bc1 COMPLEX - MECHANISTIC AND PHYSIOLOGICAL IMPLICATIONS." Journal of Biological Chemistry 280(41):34654-34660.