Mitochondria and respiratory chains SBS-922 Membrane Proteins John F. Allen School of Biological and Chemical Sciences, Queen Mary, University of London

The Respiratory Chain Includes Three Large Enzyme Complexes Embedded in the Inner Membrane Molecular Biology of the Cell Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, and Peter Walter. 2002

Not forgetting complex II…

ESCOBAR GALVIS, M L, ALLEN, J F and HÅKANSSON, G (1998) Protein synthesis by isolated pea mitochondria is dependent on the activity of respiratory complex II Current Genetics 33, In isolated pea (Pisum sativum L.) mitochondria incorporation of 35S-methionine into newly synthesised proteins was influenced by the presence of site-specific inhibitors of the respiratory electron transport chain. These effects were not produced by changes in the rate of respiratory electron transport itself nor by changes in ATP concentration. Protein synthesis was inhibited by inhibitors of ubiquione reduction but not by inhibitors of ubiquinol oxidation. By the use of additional inhibitors at specific sites of the respiratory chain, different oxidation-reduction states were obtained for the different complexes in the electron transport chain. It was found that electron transport through succinate:ubiquinone oxidoreductase (respiratory complex II) was specifically required for protein synthesis, even when all the other conditions far protein synthesis were satisfied. We suggest that a subunit of complex II, or a component closely associated with complex II, is involved in a regulatory system that couples electron transport to protein synthesis.

"Errors" in electron transfer - transfers to the "wrong" electron acceptor - occur at fixed frequency. The products of these reactions damage mitochondrial genes, which then produce defective proteins, which then make more "errors" in electron transfer....damaging more genes, making more defective proteins....and so on. The mitochondrial theory of ageing

Complex III The bc 1 -complex Complex III

Z. Zhang, L. Huang, V. M. Shulmeister, Y.-I. Chi, K.-K. Kim, L.-W. Hung, A. R. Crofts, E. A. Berry & S.-H. Kim. Electron transfer by domain movement in cytochrome bc 1 Nature 392, 677 (1998) The general features of the protein are as expected from previous biochemical and structural studies, with a large fraction corresponding to the "core" proteins (subunits I and II) on the N-side (bottom in the Fig. above), and cyt c 1 and the FeS protein on the P-side. The dimensions of the dimer are about 130 Å in diameter and 151 Å in height, with the inter-membrane space region, the transmembrane region, and the matrix region contributing about 41 Å, 35 Å and 75 Å respectively.

Two different structures from X-ray crystallography - suggesting two different positions for the head of the Rieske Fe-S protein