Electron transport mechanisms

Reumycin and xanthothricin were isolated from Actinomyces rectus bruneus and are useful as antitumor antibiotics. Methylation of reumycin resulted in the formation of the antibiotics, fervenulin, toxoflavine, and 7-methoxyreumycin. A review on their effects on an electron transport mechanism in animal and yeast cells was published in 1975 by Russian authors (75MI1, 75MI2). 

On the other hand, highly purified preparations (180-fold) obtained by Huennekens and his co-workers (H22) have been shown to be a hemo-protein with a molecular weight of approximately 185,000. With regard to these different results it is interesting that in RBC of individuals suffering from hereditary methemoglobinemia a complete lack of NAD diaphorase has been reported (S10, Sll) this would indicate the importance of an enzyme which contains FAD. The reasons for the discrepancies between the preparations obtained by two teams of investigators are not understood as yet. Perhaps they are implicated in the electron transport mechanisms or in the nature of a certain cofactor which is to be discussed now. 

The amide functionality plays an important role in the physical and chemical properties of proteins and peptides, especially in their ability to be involved in the photoinduced electron transfer process. Polyamides and proteins are known to take part in the biological electron transport mechanism for oxidation-reduction and photosynthesis processes. Therefore studies of the photochemistry of proteins or peptides are very important. Irradiation (at 254 nm) of the simplest dipeptide, glycylglycine, in aqueous solution affords carbon dioxide, ammonia and acetamide in relatively high yields and quantum yield (0.44)202 (equation 147). The reaction mechanism is thought to involve an electron transfer process. The isolation of intermediates such as IV-hydroxymethylacetamide and 7V-glycylglycyl-methyl acetamide confirmed the electron-transfer initiated free radical processes203 (equation 148). 

The electron transport mechanism in mesoporous Ti02 film is modeled mainly by using diffusion theory, except in the report by Augustinski et al.,45) who proposed the explanation that the initial film charging by dye-sensitization, in terms of the self-doping, causes an insulator-metal (Mott) transition in a donor band of Ti02, accompanied by a sharp rise in conductivity of the nanoparticles. 

Neutral square coplanar complexes of divalent transition metal ions and monoanionic chelate or dianionic tetrachelate ligands have been widely studied. Columnar stack structures are common but electrical conductivities in the metal atom chain direction are very low and the temperature dependence is that of a semiconductor or insulator. However, many of these compounds have been shown to undergo partial oxidation when heated with iodine or sometimes bromine. The resulting crystals exhibit high conductivities occasionally with a metallic-type temperature dependence. The electron transport mechanism may be located either on predominantly metal orbitals, predominantly ligand re-orbitals and occasionally on both metal and ligand orbitals. Recent review articles deal with the structures and properties of this class of compound in detail.89 90 12... 

An X-ray photoelectron spectroscopic study of Ni(DPG)2I showed no evidence of trapped valence or any appreciable change in the charge on the metal upon oxidation.97 The site of partial oxidation and hence the electron transport mechanism is still unclear but one explanation of the relatively low conductivity is that the conduction pathway is metal centred and that the M—M distances are too long for effective orbital overlap. Electron transport could be via a phonon-assisted hopping mechanism or, in the Epstein—Conwell description, involve weakly localized electronic states, a band gap (2A) and an activated carrier concentration.101... 

In this section, we describe the fabrication of metal complex oligomer and polymer wires composed of bis(terpyridine)metal complexes using the bottom-up method.11 13 This method has an advantage in fabricating organized structures of rigid redox polymer wires with the desired numbers of redox metal complexes. We also present a new electron-transport mechanism applicable to the organized redox polymer wires-coated electrode. 

A more difficult question to pursue is how electron transport occurs [38]. Three types of electron-transport mechanisms across bilayer membranes have been envisioned, including (i) direct electron tunneling from the donor to the acceptor located at the opposite membrane interfaces, (ii) electron carrier-mediated diffusional... 

Electron transport properties of metal oxides nanoparticles are very important for electrical and electronic applications as well as for understanding the unique one-dimensional carrier transport mechanism. It has been noticed that the diameter of metal oxides nanoparticles, surface conditions, crystal structure and its quality i.e., chemical composition, crystallographic orientation along the film axis etc are important parameters that influence the electron transport mechanism. It is found that conductance of a nano-structure strongly depends on their crystalline structure. For example, in the case of perfect crystalline Si nanowires having four atoms per unit cell, generally three conductance channels are found [51], One-or two-atom defect, either by addition or removal of one or two atoms may disrupt the number of such conductance channel and may cause variation in the conductance. It has been observed that change in the surface conditions of the nanowires can cause remarkable... 

Baker, M.D., Senaratne, C., and McBrien, M. 1995. Comment on intrazeolite electron transport mechanism. Journal of Physical Chemistry 99, 12367. 

Li, J.-W., Pfanner, K., and Calzaferri, G. 1995. Reply to Comment on inlrazcohlc electron transport mechanism. The importance of the manner to prepare zeolite-modified electrodes. Journal of Physical Chemistry 99, 12368-12369. 

In eukaryotic cells aerobic metabolism occurs within the mitochondrion. Acetyl-CoA, the oxidation product of pyruvate, fatty acids, and certain amino acids (not shown), is oxidized by the reactions of the citric acid cycle within the mitochondrial matrix. The principal products of the cycle are the reduced coenzymes NADH and FADH, and C02. The high-energy electrons of NADH and FADH2 are subsequently donated to the electron transport chain (ETC), a series of electron carriers in the inner membrane. The terminal electron acceptor for the ETC is 02. The energy derived from the electron transport mechanism drives ATP synthesis by creating a proton gradient across the inner membrane. The large folded surface of the inner membrane is studded with ETC complexes, numerous types of transport proteins, and ATP synthase, the enzyme complex responsible for ATP synthesis. 

In Mitchell s model protons are driven from the mitochondrial matrix across the inner membrane and into the intermembrane space by the electron transport mechanism. The energy captured from electron transport is used to create an electrical potential and a proton gradient. Because the inner membrane is impermeable to protons, they can only traverse the membrane by flowing through specific proton channels. The flow of protons through the ATP synthase drives the synthesis of ATP. (See Figure 10.1 for brief descriptions of the roles of complexes I, II, III, and IV in electron transport.)... 

The reduction of methylviologen dications to the cation-radicals at ZME (zeolite Y) interfaces shows a concentration overpotential due to the ion exchange equilibrium with sodium at the zeolite-solution interface.[98,99] In the process, methylviologen dications diffuse from the zeolite channels into solution. The authors suggest that ion exchange accounts for the electron transport mechanism. 

The NADPHj formed is very rich in energy and is able to realise the first steps of carbon dioxide assimilation. The electron transport mechanism of light reactions I and II is a noncyclic electron transfer process. Its by-product is oxygen, the formation mechanism of which is unknown. 

DHAP is also employed in the glycerophosphate shuttle, which functions as an electron-transporting mechanism in insect muscle (Figure 15.11a). 

Beilke, D., R. Weiss, F. Lohr, P. Pristovsek, F. Ffannemann, R. Bernhardt et al. (2002). A new electron transport mechanism in mitochondrial steroid hydroxylase systems based on structural changes upon the reduction of adrenodoxin. Biochemistry 41, 7969-7978. 

Figure 13.2. A proposal for a simplified classification of CYPs with reference to either use of a ferredoxin or alternative electron transport mechanism. Class la— typical bacterial system supported by ferredoxin and ferredoxin reductase, for example, CYPlOl Class Ib—Rhodococcus sp. CYP fusion protein containing a ferredoxin domain Class Ic—Methylococcus capsulatus CYPS 1-ferredoxin fusion . Class 11a— typical eukaryotic CYP/NADPH-cytochrome P450 reductase system Class lib—a fusion protein of a CYP and flavoprotein reductase, for example, P450gM 3 Class IIc—P450 j containing separate flavodoxin and flavodoxin reductase partners . Class fll—standalone functional CYPs, for example, P450jj. ...

Mineral ions participate in a wide variety of metabolic processes, electron transport mechanisms, and in nitrate reduction. By manipulation of the level of inorganic elements and ions in the nutrient medium, it is possible to influence the constituents in plants. For over 100 years, tobacco scientists have employed a fundamental research approach in attempts to understand the complex physiology and biochemistry of tobacco involved in the biosynthesis of compounds in tobacco (3973). Their efforts have greatly improved the economics of tobacco production and have led to advancements in understanding of health issues associated with tobacco and its various commercial uses (20A20). 

Cyanide causes intracellular hypoxia by inhibiting the intracellular electron transport mechan-... 

Electron transport systems perform important functions concerning respiration and energy metabolism in eucaryotes [22, 23], The electron transport reactions occur at the mitochondria inner membrane formed by electron transport proteins [24] and the lipid bilayer built up by the self-assembly of phospholipids as vital smfactants [25, 26]. The electron transport proteins include redox catalysts such as nicotinamide, iron [27, 28], and quinones [29]. The electrons produced by these redox reactions transfer through the lipid bilayer. While the relationship between the electron transport mechanisms and the molecular self-assembly in vivo has been clarified, control of the self-assembly by electron transport has been applied for an artificial polymeric surfactant. 

The chemical structure of electrically conducting polypyrrole films doped with p-toluene sulfonate and dodecyl sulfate was studied by FT-Raman spectroscopy. The spectra were compared with those from the corresponding reduced polymers after dedoping and found to be consistent with polaron and bipolaron descriptions of the electron transport mechanism in polypyrrole (331). 

The deciding hint for explaining the basic electron transport mechanism in conductive polymers came from studies with nanoparticles of conventional metals like indium, silver, or copper. Nimtz et al. [4] found in 1989 that metallic particles, if prepared on a nanoscale of below 1 p,m down to 10 nm, show some distinct deviations from macroscopic metals (see Figure 1.2). 

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