Electrons in DNA

In closing, it may be instructive to contrast the electron-transfer events taking place in polypeptides with those we have been studying relating to electrons in DNA [14]. In these studies, we simulate processes in which... 

The majority of experiments on charge transfer in DNA deal with hole transfer. There are only few experimental studies pertaining to the transfer of excess electrons in DNA [89-91]. Theoretical studies focused on electron affinities of bases and their complexes [92-95]. 

When estimating the energetics of excess electron transfer in DNA via differences of electron affinities (EA) of nucleobases B in WCP trimers 5 -XBY-3 [92], we found the EA values of bases to decrease in the order C T A>G. The destabihzing effect of the subsequent base Y is more pronounced than that of the preceding base X. As strongest electron traps, we predicted the sequences 5 -XCY-3 and 5 -XTY-3, where X and Y are pyrimidines C and T. These triads exhibit very similar EA values, and therefore, the corresponding anion radical states should be approximately in resonance, favoring efficient transport of excess electrons in DNA [92]. 

So far we have seen that ionization creates a hole and ejects and electron. In DNA the electron is captured exclusively by the pyrimidine bases while the holes are distributed between guanine and the deoxyribose. The next problem to solve is to determine the free radical yield in DNA and to correlate this yield with the yield of strand breaks. These are very challenging experiments since there are so many factors influencing radicals yield. 

Wagenknecht H.-A., Reductive electron transfer and transport of excess electrons in DNA, Angew. Chem. Int. Ed., 2003,42, 2454-2460. 

When induced in macrophages, iNOS produces large amounts of NO which represents a major cytotoxic principle of those cells. Due to its affinity to protein-bound iron, NO can inhibit a number of key enzymes that contain iron in their catalytic centers. These include ribonucleotide reductase (rate-limiting in DNA replication), iron-sulfur cluster-dependent enzymes (complex I and II) involved in mitochondrial electron transport and cis-aconitase in the citric acid cycle. In addition, higher concentrations of NO,... 

Flavins — Riboflavin is first of all essential as a vitamin for humans and animals. FAD and FMN are coenzymes for more than 150 enzymes. Most of them catalyze redox processes involving transfers of one or two electrons. In addition to these well known and documented functions, FAD is a co-factor of photolyases, enzymes that repair UV-induced lesions of DNA, acting as photoreactivating enzymes that use the blue light as an energy source to initiate the reaction. The active form of FAD in photolyases is their two-electron reduced form, and it is essential for binding to DNA and for catalysis. Photolyases contain a second co-factor, either 8-hydroxy-7,8-didemethyl-5-deazariboflavin or methenyltetrahydrofolate. ... 

Ullrich S, Schultz T, Zgierski MZ, Stolow A (2004) Electronic relaxation dynamics in DNA and RNA bases studied by time-resolved photoelectron spectroscopy. Phys Chem Chem Phys 6 2796... 

Jean JM, Hall KB (2002) 2-aminopurine electronic structure and fluorescence properties in DNA. Biochem 41 13152-13161... 

Extended solid state n systems facilitate CT, particularly when doped [4-6]. The analogy between DNA and conductive solid state -stacks therefore establishes that a requisite condition for CT may exist in DNA. DNA contains an array of heterocyclic aromatic base pairs, stacked at a distance of 3.4 A, wrapped within a negatively charged sugar phosphate backbone [7] (Fig. 1). The interactions between the n electrons of the DNA base pairs provide the electronic coupling necessary for CT to occur. 

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