CRYSTALLIZATION AND PRELIMINARY STRUCTURE OF BEEF-HEART MITOCHONDRIALCYTOCHROME-BC(1) COMPLEX

The method reported for isolation of ubiquinol-cytochrome-c reductase complex from submitochondrial particles was modified to yield a prepar ation for crystallization. The cytochrome bc(1) complex was first crys tallized in large thin plate form and diffracts X-rays to 7 Angstrom r esolution in the presence of mother liquor. This crystalline complex w as enzymatically active and contains ten protein subunits. It had 33 m ol phospholipid and 0.6 mol ubiquinone per mol protein. With slightly modified crystallization conditions, different crystal forms were obta ined. Crystals grown in the presence of 20% glycerol diffracted X-rays up to 2.9 Angstrom resolution using a a synchrotron source. Four heav y atom derivatives have been obtained. The 3-D structure of the cytoch rome bc(1) complex was solved to 3.4 Angstrom resolution. Crystalline cytochrome bc(1) complex is a dimer: most of the masses of core protei ns I and II protrudes from the matrix side of the membrane, whereas th e cytochrome b protein is located mainly within the membrane. There ar e 13 transmembrane helices in each monomer. Most of the mass of cytoch rome c(1) and iron-sulfur protein including their redox centers are lo cated on the cytoplasmic side of the membrane. The distances between t hese redox centers have been determined, and several electron transfer inhibitor binding sites in the complex have been located.