7.1.1.6 - 7.1.1.6 3.0 A crystal structure, native enzyme and enzyme in complex with 8-hydroxy-5,7-dimethoxy-3-methyl-2-tridecyl-4H-chromen-4-one or with 2,5-dibromo-5-methyl-6-isopropyl-benzoquinone 7.1.1.6 free enzyme and enzyme complexed with with quinone analogue inhibitors tridecyl-stigmatellin and 2-nonyl-4-hydroxyquinoline N-oxide, X-ray diffraction structure determination at 2.70 A, 3.07 A, and 3.25 A resolution, respectively 7.1.1.6 hanging drop vapour diffuion method, 0.0015 ml protein solution, containing 0.135-0.18 mM protein, is mixed with 0.0015 ml of reservoir solution, containing 100 mM Tris-HCl, pH 8.5, 200 mM MgCl2, 40 mM CdCl2, and 16?17% PEG-550 monomethyl ether, 4 °C, hexagonal bipyramidal crystals appear in 24?36 h, X-ray diffraction structure determination at 2.8 A resolution 7.1.1.6 hanging drop vapour diffusion method using 1.5 M [NH4]2SO4, 100 mM sodium acetate at pH 4.6 7.1.1.6 hanging drop, vapor-diffusion method 7.1.1.6 hanging-drop vapor diffusion. A native structure of the cytochrome b6f complex with improved resolution is obtained from crystals of the complex grown in the presence of divalent cadmium 7.1.1.6 modeling of the first step of plastoquinol PQH2 oxidation by the iron-sulfur protein of the Cyt b6f complex. The H-transfer reaction displays a bidirectional mechanism, an electron is directed to the Fe(1) atom of the [Fe2S2] cluster of the iron-sulfur protein, and a proton is accepted by the Nepsilon atom of the His155 residue liganding the Fe(1) atom. Results support a diabatic model of the H-transfer, which implies that the elementary steps of electron and proton transfer occur much more rapidly than the concomitant changes in the system geometry 7.1.1.6 vapour diffusion hanging drop method, X-ray structure at 3.1 A