Figure 26.3 The most important regions of secondary structure, (a)* α helix and (b)* β sheet, showing hydrogen bonding between main-chain amide and carbonyl groups and their corresponding representations.

Figure 26.4 Illustrations of how protein structures are represented to reveal either (left)* secondary structure or (right)* the filling of space by nonhydrogen atoms. The example shows the four subunits of the K+ channel, which is found mainly embedded in the cell membrane.

Figure 26.10* Zinc fingers are protein folds that form a sequence able to bind
to DNA. A typical finger is formed by the coordination of Zn(II) to two pairs of amino acid side chains located either side of the ‘fingertip’.

Figure 26.11* A pair of zinc fingers interacting with a
section of DNA.

Figure 26.13* Structure of the Fe- transport protein transferrin: the identical halves of the molecule each coordinates to a single Fe(III) atom (the black spheres) between two lobes. This coordination causes a conformational change that allows transferrin to be recognized by the transferrin receptor.

Figure 26.14* The structure of ferritin, showing the arrangement of subunits that make up the protein shell.

Figure 26.15* Structure of myoglobin, showing the Fe–porphyrin group located between helices E and F.

Figure 26.16* Reversible binding of O2 to myoglobin: coordination by O2 causes the Fe to become low-spin and move into the plane of the porphyrin ring.

Figure 26.18* Haemoglobin is an α2β2 tetramer. Its α and β subunits are very similar to myoglobin. Haem groups are shown in black.

Figure 26.25* Different views (but from the same viewpoint) of mitochondrial cytochrome c: (a) the secondary structure and the position of the haem cofactor; (b) the surface charge distribution that guides the docking with its natural redox partners (red and blue areas represent patches of negative and positive charge, respectively).

Figure 26.26* The bimolecular ET complex between cytochrome c and cytochrome c peroxidase produced by co-crystallization of cytochrome c with the Zn derivative of cytochrome c peroxidase. The orientation suggests an electron-transfer pathway between the haem groups of cytochrome c and cytochrome c peroxidase that includes tryptophan.

Figure 26.27* A series of three FeeS clusters provides a long-range electron transfer pathway to the buried active site in hydrogenases.

Figure 26.28* The plastocyanin molecule.

Figure 26.29* The active site of carbonic anhydrase.

Figure 26.34* The active site of yeast cytochrome c peroxidase showing amino acids essential for activity and indicating how peroxide is bound in the distal pocket.

Figure 26.41 The [4MnCa-5O] active site of photosynthetic O2 production. The Ca atom is shown in green, Mn atoms are shown in mauve, and O atoms are shown in red.