Copper electron-transport

Complexes III and IV have Fe-porphyrin prosthetic groups (hemes), complex IV also contains copper atoms which are involved in electron transport. Complexes I, III, and IV use the energy of electron transport to pump protons out of the matrix so as to maintain a pH gradient and an electrical potential difference across the inner membrane required for ATP synthesis (see below and Appendix 3). It is important to remember that all dehydrogenations of metabolic substrates remove two protons as well as two electrons and that a corresponding number of protons are consumed in the final reduction of dioxygen (Figures 5, 6). 

Organic semiconductors are becoming increasingly important in the fabrication of electronic devices. For electron transport, metal complex pigments, such as hexa-deca-fluoro copper phthalocyanine (76), are showing potential.79... 

A typical multilayer thin film OLED is made up of several active layers sandwiched between a cathode (often Mg/Ag) and an indium-doped tin oxide (ITO) glass anode. The cathode is covered by the electron transport layer which may be A1Q3. An emitting layer, doped with a fluorescent dye (which can be A1Q3 itself or some other coordination compound), is added, followed by the hole transport layer which is typically a-napthylphenylbiphenyl amine. An additional layer, copper phthalocyanine is often inserted between the hole transport layer and the ITO electrode to facilitate hole injection. 

IV. Superoxide dismutase (EC 1.15.1.1) Within a cell the superoxide dismutases (SODs) constitute the first line of defense against ROS. Superoxide radical (02) is produced where an electron transport chain is present, as in mitochondria and chloroplasts, but 02 activation may occur in other subcellular locations such as glyoxysomes, peroxisomes, apoplast and the cytosol. Thus SODs are present in all these cellular locations, converting superoxide into hydrogen peroxide and water (i.e. copper/zinc SODs are typically found in the nuclei and cytosol of eukaryotic cells). 

Electronic spectra of metalloproteins find their origins in (i) internal ligand absorption bands, such as n->n electronic transitions in porphyrins (ii) transitions associated entirely with metal orbitals (d-d transitions) (iii) charge-transfer bands between the ligand and the metal, such as the S ->Fe(II) and S ->Cu(II) charge-transfer bands seen in the optical spectra of Fe-S proteins and blue copper proteins, respectively. Figure 6.3a presents the characteristic spectrum of cytochrome c, one of the electron-transport haemoproteins of the mitochondrial... 

BLUE COPPER PROTEINS INVOLVED IN ELECTRON TRANSPORT... 

In many crucial biological processes, such as oxygen transport, electron transport, intermediary metabolism, metals play an important part. Therefore, disorders of metal homeostasis, metal bioavailability or toxicity caused by metal excess, are responsible for a large number of human diseases. We have already mentioned disorders of iron metabolism (see Chapter 7) and of copper metabolism (see Chapter 14). The important role, particularly of redox metals such as copper and iron, and also of zinc, in neurodegenerative diseases, such as Parkinson s disease, Alzheimer s disease, etc. has also been discussed (see Chapter 18). We will not further discuss them here. 

Blue Copper Proteins Involved in Electron Transport. 

Most mechanisms which control biological functions, such as cell respiration and photosynthesis (already discussed in Chapter 5, Section 3.1), are based on redox processes. In particular, as shown again in Figure 1, it is evident that, based on their physiological redox potentials, in photosynthesis a chain of electron carriers (e.g. iron-sulfur proteins, cytochromes and blue copper proteins) provides a means of electron transport which is triggered by the absorption of light. 

Finally, we examine azurin, a blue protein (FW = 14 000) devoted to bacterial electron transport, the copper centre of which has a penta-coordinate trigonal bipyramidal geometry, at variance with all the other cupredoxins, Figure 39.73... 

Plastocyanin from parsley, a copper protein of the chloroplast involved in electron transport during photosynthesis, has been reported to have a fluorescence emission maximum at 315 nm on excitation at 275 nm at pH 7 6 (2°8) gjncc the protein does not contain tryptophan, but does have three tyrosines, and since the maximum wavelength shifts back to 304 nm on lowering the pH to below 2, the fluorescence was attributed to the emission of the phenolate anion in a low-polarity environment. From this, one would have to assume that all three tyrosines are ionized. A closer examination of the reported emission spectrum, however, indicates that two emission bands seem to be present. If a difference emission spectrum is estimated (spectrum at neutral pH minus that at pH 2 in Figure 5 of Ref. 207), a tyrosinate-like emission should be obtained. 

Mammalian COX (the illustration shows the enzyme from bovine heart) is a dimer that has two identical subunits with masses of 204 kDa each. Only one subunit is shown in detail here the other is indicated by gray lines. Each subunit consists of 13 different polypeptides, which all span the inner mitochondrial membrane. Only polypeptides I (light blue) and II (dark blue) and the linked cofactors are involved in electron transport. The other chains, which are differently expressed in the different organs, probably have regulatory functions. The two heme groups, heme a (orange) and heme ai (red) are bound in polypeptide 1. The copper center Cua consists of two copper ions (green), which are coordinated by amino acid residues in polypeptide II. The second copper (Cub) is located in polypeptide I near heme... 

Blue copper proteins, 36 323, 377-378, see also Azurin Plastocyanin active site protonations, 36 396-398 charge, 36 398-401 classification, 36 378-379 comparison with rubredoxin, 36 404 coordinated amino acid spacing, 36 399 cucumber basic protein, 36 390 electron transfer routes, 36 403-404 electron transport, 36 378 EXAFS studies, 36 390-391 functional role, 36 382-383 occurrence, 36 379-382 properties, 36 380 pseudoazurin, 36 389-390 reduction potentials, 36 393-396 self-exchange rate constants, 36 401-403 UV-VIS spectra, 36 391-393 Blue species... 

Electron-transferring subunit, nickel-containing hydrogenases, 38 409-410 Electron transport blue copper proteins, 36 378 NiFe hydrogenase, 47 16-17 Electron volt, 16 73... 

Cytochrome c and Cytochrome c Oxidase. - The mitochondrial electron transport chain is the site at which most of the free energy to be obtained from the oxidation of substrates is released and conserved as the energy-rich molecule ATP. In the final stage of this process, CcO, which is supplied with electrons by cyt c, catalyses the four-electron reduction of oxygen to water. Both are haem proteins, with CcO containing two haem and three copper centres, and both exhibit peroxidase-type activity. 

Ceruloplasmin is involved in copper storage and transport as well as in iron mobilisation and oxidation. Among the blue oxidases it is unique since it contains, in addition to the usual motif of a type 1 combined with the trinuclear cluster, two other type 1 coppers. Electron transfer occurs, however, only between five of the six copper ions since one of the type 1 centres is not catalytically relevant due to its too high redox potential. The redox potentials of the centres were determined and possible electron transfer pathways among the copper sites were discussed.101... 

These complexes are usually named as follows I, NADH-ubiquinone oxidoreductase II, succinate-ubiquinone oxidoreductase III, ubiquinol-cytochrome c oxidoreductase IV, cytochrome c oxidase. The designation complex V is sometimes applied to ATP synthase (Fig. 18-14). Chemical analysis of the electron transport complexes verified the probable location of some components in the intact chain. For example, a high iron content was found in both complexes I and II and copper in complex IV. 

Why did nature pick iron, and to a much lesser degree copper, rather than calcium, magnesium, potassium, and so forth for roles in the electron-transport... 

Current state-of-the-art hole-transport and electron-transport materials [50] are shown in Figure 6.15. Hole-transport materials include oligo- (58) and polythiophenes (59) [51], poly(thienylene vinylenes) (60) [52], and pentacenes [53] (61). Electron-transport materials include copper phthalocyanine (3), hexadeca-fluoro copper phthalocyanine (62), naphthalenetetracarboxy dianhydride (63), and perylene tetracarboxy dianhydride (64). 

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