1. Methods to Study Metals in Biological Systems
Chapter 6
Methods to Study Metals in Biological Systems
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FIGURE 6.1 (a) EPR spectrum of horse spleen apoferritin incubated with haemin (8 haemin molecules/molecule of apoferritin) at pH 8; (b) EPR spectrum of horse spleen apoferritin 20 iron atoms/molecule of apoferritin at pH 4; (c) EPR spectrum of horse spleen apoferritin incubated with haemin (8 haemin molecules/molecule of apoferritin) in sodium phosphate buffer, 0.1 M, pH 8, dialysed against sodium acetate buffer, 0.1 M, pH 5.3, crystallised with ammonium sulfate and cadmium sulfate and the crystals then re-dissolved in water; (d) EPR spectrum of horse spleen apoferritin incubated with haemin (8 molecules of haemin/molecule of apoferritin) in sodium phosphate buffer, 0.1 M, pH 8, dialysed against sodium acetate buffer 0.1 M, pH 5.3; (e) the signal 3d was simulated as an effective S  1/2 system with g-strain. The intensity was corrected for the Boltzmann population over the three doublets of the S  5/2 system assuming a zero-field splitting D  2 cm-1 i.e., 34% population of the middle doublet for a temperature of 16 K. Similarly, the intensity of the g  6 signal from the lowest Kramers doublet of an axial S  5/2 system was corrected assuming D  10 cm-1, i.e., 84% population of the mS  1/2 doublet at 16 K. For all spectra, frequency: 9.41 GHz, temperature: 16 K. (From Carette et al., Copyright 2006 with permission from Elsevier.)
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FIGURE 6.2 Mössbauer spectra of human haemosiderin (a), prehaemosiderin (b), haemosiderin from iron-loaded rats (c), and horse haemosidin (d). (From Ward et al., Copyright 1994 with permission from John Wiley and Sons.)
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FIGURE 6.3 AtxA and Ccc2 exchanging a Cu(I) ion. (From Fragai, Luchinat and Parigi, et al., Copyright 2006 with permission from the American Chemical Society.)
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FIGURE 6.4 (a) Visible absorption spectrum of cytochrome c in its reduced and oxidised states. (b) The three separate -bands in the visible spectrum of beef heart mitochondria (below) indicating the presence of cytochromes a, b, and c, with the spectrum of cytochrome c (above) as reference.
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FIGURE 6.5 Absorption spectrum (a) and CD spectrum (b) of the Fe4S4 cluster of a high-potential iron protein (HiPIP- from Chromatium sp.). (From Cowan, Copyright 1997 with permission from John Wiley and Sons.)
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FIGURE 6.6 Ferroxidase site in reduced Bacterioferritin from Desulfovibrio desulfuricans with ironligand distances in ångströms: (a) as determined by crystallography, (b) adjusted to give agreement with the EXAFS. Grey, carbon; red, oxygen; blue, nitrogen; orange, iron; hydrogens are omitted for clarity. Green and blue distance values refer to FeA (left iron ion) and FeB (right), respectively. (From Toussaint et al., Copyright 2009 with permission from Springer.)
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FIGURE 6.7 The structure of Bacillus brevis Dps dodecamer. (a) The BbDps dodecamer. The 12 subunits are shown by the ribbon representation of their C traces. The 24 iron ions at the ferroxidase centres inside the protein shell are shown as red spheres. (b) Ribbon diagram of the BbDps monomer. Helices I V are shown in different colours. (c) A BbDps dimer. The iron ions in the two ferroxidase centres at the dimer interface are shown as red spheres. The helices are coloured as in (b). (From Ren et al., Copyright 2003 with permission from Elsevier.)
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FIGURE 6.8 The di-nuclear ferroxidase centre Bacillus brevis Dps dodecamer. (a) Electron densities at one of the di-nuclear ferroxidase centres at the dimer interface. The (2FoFc) map is coloured in light blue and contoured at the 1.4 level. The two iron ions have the highest density values in the map, which are 12.7 and 7.2. The existence of two water molecules at the di-iron site is revealed by the superimposed (FoFc) map, which is coloured in red and contoured at the 4.0 level. The iron ions and water molecules are shown as spheres, coloured in magenta and light orange, respectively. (b) A drawing of the coordination of the iron ions at the di-nuclear centre. The coordination is indicated by dotted lines and distances (in Å). (From Ren et al., Copyright 2003 with permission from Elsevier.)
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