Nitration, guanine

Tuo J, Liu L, Poulsen HE, Weimann A, Svendsen O, Loft S (2000) Importance of guanine nitration and hydroxylation in DNA in vitro and in vivo. Free Radic Biol Med 29 147-155... 

Scheme 3 Nitration of guanine in single-stranded DNA via combination of the photo-chemically generated G(-H) and NO2 radicals...

J.C. Niles et al., Peroxynitrite-induced oxidation and nitration products of guanine and 8-oxoguanine Structures and mechanisms of product formation. Nitric Oxide 14, 109-121... 

Sodum, R.S., Fiala, E.S. (2001). Analysis of peroxynitrite reactions with guanine, xanthine, and adenine nucleosides by high-pressure liquid chromatography with electrochemical detection C8-nitration and oxidation. Chem. Res. Toxicol. 14 438-50. 

The enzyme contains two heme A molecules, two heme C molecules, one molybdenum atom, and five [Fe4S4] clusters in the molecule with molecular mass of 250 kDa. Molybdenum occurs as a complex with molybdopterin guanine dinucleotide (MGD) (Fukuoka et al 1987 Yoshino, 1994 Suzuki et al., 1997). The enzyme catalyzes the reduction of N. winogradskyi ferricytochrome c-550 and horse ferricytochrome c with nitrite, i.e it catalyzes the oxidation of nitrite with ferricytochromes c as the electron acceptor. The reaction is stimulated by Mn2+ and Ca2+. Although the enzyme catalyzes actively the oxidation of nitrite around pH 8, it shows also capability to catalyze the reduction of nitrate with ferrocytochrome c at pHs less than 6 the bacterium changes itself from a nitrifier to a denitrifieT at pHs less than 6. 

In the heterotrophic nitrate respiration, in most cases hydrogen atoms derived from organic compounds ([H], mostly in the form of NADH in the case of heterotrophic denitriliers) are first oxidized with nitrate. The reaction is catalyzed by nitrate reductase. The enzyme contains Mo, [Fe4S4] and [Fe2S2] clusters (Fe/S), and cytochrome b (Chaudhry and MacGregor, 1983). Mo is present in the enzyme as molybdenum cofactors combining with molybdopterin or molybdopterin guanine dinucleotide. The enzyme catalyzes the reduction of nitrate to nitrite with ubiquinol or menaquinol (QH2) as the electron donor. 

We must now consider how the various "aquo species" interact with the DNA bases. So far, we have examined interactions of thymine, uracil and cytosine in detail and to a lesser extent with guanine. Reaction products from the aqueous solution produced by silver nitrate treatment of the chloride-complexes are complex mixtures, which is hardly surprising based on the known conq)lexity of the aqueous solution. It is possible to prepare monomeric (NHj)2 PtCbase " species similar to those obtained from the direct" reaction ot cis-PtCk (NH ) and the bases we assume they come from monomerxc aquo-complexes. 

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