Biological electron transfer chain

Cytochromes serve as electron donors and electron acceptors in biological electron transfer chains, and with >75,000 members (53) they provide the bulk of natural heme proteins in biology. Cytochromes may be fixed into place within an extended electron transfer chain, such as the membrane-bound 6l and 6h of the cytochrome bci complex, or may be soluble and act as mobile electron carriers between proteins, for example, cytochrome c (54). In either role, the cytochrome may be classified by the peripheral architecture of the porphyrin macrocycle. Figure 1 shows the dominant heme types in biological systems, which are hemes a, b, c, and d, with cytochomes b and c being most prevalent. The self-association of a protein with heme via two axial ligands is a... 

P.L. Dutton, NATO/ESF Workshop Biological Electron-Transfer chains, Tomar, Portugal (1997). 

J.A. Duine and A. Hacisalihoglu, in Biological Electron-Transfer Chains (G.W. Canters and E. Vijgenboom, Eds.) Kluwer Academic Publishers, Dordrecht, NATO ASI Series C, vol. 512, pp. 149-164. 

S. S. Skourtis and D. N. Beratan in Biological Electron Transfer Chains Genetics, Composition, and Mode of Operation, GW Canters and E Vijgenboom (eds) Kluwer Academic Publishers, The Netherlands (1998). 

In conclusion, the PSII-Ti02 system represents a bioelectronic prototype that achieves the coupling of a biological electron transfer chain with an inorganic semiconductor device, which should convert light both to electrical and chemical energy. 

Baymann F, Moss DA, Mantele W (1991) An electrochemical assay for the characterization of redox proteins from biological electron-transfer chains. Anal Biochem 199 269-274... 

To transfer electrons over extended distances between catalytic sites of substrate oxidation and reduction and sites of energy conversion. Nature relies on redox chains. The use of chains allows biological electron transfer to escape the exponential decrease of rate with distance, and to recover an essentially linear dependence of rate over very long distances, keeping tunneling rates faster than the kcat of the enzymes. 

Electron Transfer Chain, Chemistry of Hemes in Biology... 

Electron Transfer Chain, Chemistry of Metabolic Diseases, Chemical Biology of Mitochondria, Structural Dynamics of Mitochondrial Proteomics Oxidative Metabolism, Chemistry of... 

If the dominant electron transfer at low temperature is from the considerably more distant Heme2 (24.6 A), why is the rate as fast as a millisecond and not the 10-to 100-ms timescale typical for these distances, packing densities and driving forces (Eq. 3) Furthermore, at moderate potentials when Kernel and Heme3 are reduced but the much lower potential Heme2 in between is oxidized, how can Heme3 reduce photo-oxidized Kernel To address these questions we need to look into the role of electron transfer chains in biological systems. 

In 1961 Bob Williams was the first to point out that the role of hydrogen in biology, in bound and protonic forms, made it the ideal element for coupling both metabolic and proton energies to the formation of ATP. The connection made depended upon his realization of the importance of electron-transfer chains in biology and therefore a fundamental role for iron. A long exchange of views with Dr. P. Mitchell has followed. 

Without biological electron transfer reactions (also called reduction/oxidation or redox reactions) life would not exist. Well-organized electron transfer reactions in a series of membrane-bound redox proteins form the basis for energy conservation in photosynthesis and respiration. The basic reaction is simply the transfer of electrons from the donor to the final electron acceptor. Perhaps the best example of these redox reactions, their importance for living organisms, and the nature of the different type of biocatalysts that are involved is the respiration chain present in the membranes of mitochondria. The membrane-bound nature of this electron transport chain, supporting electron transfer from NADH to O2 as... 

Cytochrome c3 is distinct from the class I c-type cytochromes (for example, mitochondrial cytochrome c) and class II c-type cytochromes (for example, cytochrome cf) in terms of out-of-plane ligation. The class III cytochromes have histidine in both the fifth and sixth heme coordination positions versus his-met (class I) or his-vacant (class II) and also differ in the number of covalently bound heme groups per peptide chain four heme groups for class III versus one heme group for classes I and II. Moreover, the cytochromes c3 have a number of unusual properties that make them valuable experimental materials for understanding biological electron transfer. 

A primary intracellular target for the biological actions of nitric oxide ( NO) production is intracellular iron (Hibbs et al., 1990 Henry et al., 1993). In activated macrophages and their tumor cell targets, a characteristic pattern of metabolic dysfunction is observed as a result of -NO synthesis, which includes loss of nonheme iron-containing enzyme function, including aconitate hydratase, complexes I and II of the mitochondrial electron transfer chain (Hibbs et al., 1990) as well as the nonheme iron-containing enzyme ribonucleotide reductase (Lepoivre et al., 1991). 

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