Subject adenine, protonated

Working at 3.0T with proton decoupling, Sevastianova et al. partially resolved the resonance of nicotinamide adenine dinucleotide phosphate (NADPH) from that of a-NTP. ° NADPH was higher in subjects with nonalcoholic steatohepatitis and cirrhosis than in healthy controls and correlated with disease severity. Solga et al. investigated the reliability of both and P MRS at 1.5 T in cohorts of obese diabetic subjects and healthy con-trols. ° Whereas hepatic fat could be reliably measured with relative ease, hepatic ATP proved difficult with obese subjects due to reduced P SNR. 

Figure 1 The mitochondrial respiratory chain. Electron transfer (brown arrows) between the three major membrane-bound complexes (I, III, and IV) is mediated by ubiquinone (Q/QH2) and the peripheral protein c)dochrome c (c). Transfer of protons hnked to the redox chemistry is shown by blue arrows red arrows denote proton translocation. NAD+ nicotinamide adenine dinucleotide, FMN flavin mononucleotide, Fe/S iron-sulfur center bH,bi, and c are the heme centers in the cytochrome bc complex (Complex III). Note the bifurcation of the electron transfer path on oxidation of QH2 by the heme bL - Fe/S center. Complex IV is the subject of this review. N and P denote the negatively and positively charged sides of the membrane, respectively...

The ability of adenine and cytosine to undergo reduction in aqueous medium is at least partially retained at the level of oligo- and polynucleotides. In both acid and neutral media, such residues in single-stranded RNA, DNA and synthetic polynucleotides, when subjected to d.c. polarography, undergo irreversible reduction in a protonated, adsorbed, state with the transfer of four electrons to adenine... 

There are various forms of tautomerism which operate in the different purine species. (1) Prototropy which involves attachment of the proton to any one of the four ring nitrogen atoms (Scheme 5). Corresponding CH tautomers, for example (52), seem to be of little significance. (2) Amine-imine tautomerism which operates in the aminopurines such as adenine (Scheme 6). (3) Lactam-lactim tautomerism as in the hydroxypurines such as hypoxanthine (Scheme 7) and the related thioxo-thiol tautomerism (53) and (54) in the biologically imporfant mercaptopurines (Scheme 8). The subject has recently been discussed in some detail <76AHC(Si)502>. 

More than 150 crystal structures of purines, many of them related to adenine and guanine, have been published, These investigations have been expanded to cover nucleosides, nucleotides and other purine derivatives. The data are the subject of a recent review and also an earlier report. " The X-ray data of both neutral and protonated forms of adenine and guanine derivatives have been reported. -... 

During the last two years, monohydrated forms (including the geometries of the water assisted transition states for intramolecular proton transfer) of the 7H-and 9H- adenine (the B3LYP/6-31 l(d,p) level), cytosine (MP2/6-31 G(d) level) and mono and dihydrated forms of 7H- and 9H- guanine (MP2/6-31 G(d) level) have been studied extensively [119 -124]. Furthermore, the post Hartree - Fock investigations of the struetural parameters of the isolated DNA bases are the subject of a large number of publications (for the reviews see [61,125]). 

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