TY - JOUR AB - For any number field k, upper bounds are established for the number of k-rational points of bounded height on non-singular del Pezzo surfaces defined over k, which are equipped with suitable conic bundle structures over k. AU - Browning, Timothy D AU - Swarbick Jones, M ID - 166 JF - Proceedings of the Bonn session in analytic number theory and diophantine equations TI - Counting rational points on del Pezzo surfaces of degree 5 VL - 360 ER - TY - JOUR AB - The molecular organization of bacterial NADH: ubiquinone oxidoreductase (complex I or NDH-1) is not established, apart from a rough separation into dehydrogenase, connecting and membrane domains. In this work, complex I was purified from Escherichia coli and fragmented by replacing dodecylmaltoside with other detergents. Exchange into decyl maltoside led to the removal of the hydrophobic subunit NuoL from the otherwise intact complex. Diheptanoyl phosphocholine led to the loss of NuoL and NuoM subunits, whereas other subunits remained in the complex. The presence of N,N-dimethyldodecylamine N-oxide or Triton X-100 led to further disruption of the membrane domain into fragments containing NuoL/M/N, NuoA/K/N, and NuoH/J subunits. Among the hydrophilic subunits, NuoCD was most readily dissociated from the complex, whereas NuoB was partially dissociated from the peripheral arm assembly in N,N-dimethyldodecylamine N-oxide. A model of subunit arrangement in bacterial complex I based on these data is proposed. Subunits NuoL and NuoM, which are homologous to antiporters and are implicated in proton pumping, are located at the distal end of the membrane arm, spatially separated from the redox centers of the peripheral arm. This is consistent with proposals that the mechanism of proton pumping by complex I is likely to involve long range conformational changes. AU - Holt, Peter J AU - Morgan, David J AU - Leonid Sazanov ID - 1959 IS - 44 JF - Journal of Biological Chemistry TI - The location of NuoL and NuoM subunits in the membrane domain of the Escherichia coli Complex I: implications for the mechanism of proton pumping VL - 278 ER - TY - JOUR AB - NADH-ubiquinone oxidoreductase (complex I or NDH-1) was purified from the BL21 strain of Escherichia coli using an improved procedure. The complex was effectively stabilized by addition of divalent cations and lipids, making the preparation suitable for structural studies. The ubiquinone reductase activity of the enzyme was fully restored by addition of native E. coli lipids. Two different two-dimensional crystal forms, with p2 and p3 symmetry, were obtained using lipids containing native E. coli extracts. Analysis of the crystals showed that they are formed by fully intact complex I in an L-shaped conformation. Activity assays and single particle analysis indicated that complex I maintains this structure in detergent solution and does not adopt a different conformation in the active state. Thus, we provide the first experimental evidence that complex I from E. coli has an L-shape in a lipid bilayer and confirm that this is also the case for the active enzyme in solution. This suggests strongly that bacterial complex I exists in an L-shaped conformation in vivo. Our results also indicate that native lipids play an important role in the activation, stabilization and, as a consequence, crystallization of purified complex I from E. coli. AU - Leonid Sazanov AU - Carroll, Joe D AU - Holt, Peter J AU - Toime, Laurence J AU - Fearnley, Ian M ID - 1960 IS - 21 JF - Journal of Biological Chemistry TI - A role for native lipids in the stabilization and two dimensional crystallization of the Escherichia coli NADH ubiquinone oxidoreductase (complex I) VL - 278 ER - TY - JOUR AU - Timothy Browning ID - 205 IS - 3 JF - Acta Arithmetica TI - Counting rational points on cubic and quartic surfaces VL - 108 ER - TY - JOUR AB - Let T ⊂ ℙ 4 be a non-singular threefold of degree at least four. Then we show that the number of points in T(ℚ), with height at most B, is o(B 3) or B → ∞. AU - Timothy Browning ID - 206 IS - 1 JF - Quarterly Journal of Mathematics TI - A note on the distribution of rational points on threefolds VL - 54 ER -