INSIGHTS INTO THE MECHANISMS OF QUINOL OXIDATION IN CYTOCHROME bc1IN LIGHT OF THE STRUCTURE OF THE BACTERIAL COMPLEX

Abstract

The ten years since the first publication of the structure from bovine heart mitochondria in 1997 have significantly broadened our structural knowledge of cytochrome bc1and b6f complexes from various organisms under a variety of conditions providing unprecedented mechanistic insights into the function of these essential enzymes. Still many questions remain. The bifurcated electron transfer at the quinol oxidation ( QP) site is one of the most difficult and unresolved problems. Intertwined with it, the proton translocation pathway and the quinol oxidation chemistry have remained focuses of intense research. Structural studies of mitochondrial bc1complexes have not only provided an atomic view of the bc1complex, defining many critical, functionally important features such as the locations of the QPand QNsites, but have also offered a number of important clues to mechanistic issues leading to the formulation of the "conformational switch of ISP" hypothesis. Intensive biochemical, genetic, and biophysical studies coupled with structural investigations have provided strong support for this hypothesis. The recent structure determination of the bc1from the photosynthetic bacterium R. sphaeroides promises further insight.