Hypoxanthine Adenine Research Articles

The influence of Cu+ binding to hypoxanthine on stabilization of mismatches involving hypoxanthine and DNA bases: a DFT study

In the present work, the influence of Cu+ binding to N3- and N7-positions of hypoxanthine on energetic, geometrical and topological properties of hypoxanthine–guanine, hypoxanthine–adenine, hypoxanthine–cytosine, hypoxanthine–thymine and hypoxanthine–hypoxanthine mismatches is theoretically investigated. The calculations, in gas phase, are performed at B3LYP/6-311++G(3df,3pd) level of theory. Unlike the other mispairs, Cu+ binding to N3-position of hypoxanthine causes the proton transfer process from enol form of hypoxanthine to imino forms of adenine and cytosine. This process also occurs in all mismatches having enol form of hypoxanthine when Cu+ binds to N7-position of hypoxanthine. The mismatches are stabilized by hydrogen bonds. The influence of Cu+ on hydrogen bonds is also examined by atoms in molecules (AIM) and natural bond orbital (NBO) analyses.Communicated by Ramaswamy H. Sarma

Characterization of the NADH dehydrogenase and fumarate reductase of Fibrobacter succinogenes subsp. succinogenes S85

Conditions promoting maximal in vitro activity of the particulate NADH:fumarate reductase from Fibrobacter succinogenes were determined. This system showed a pH optimum of 6.0 in K+ MES buffer only when salt (NaCl or KCl) was present. Salt stimulated the activity eightfold at the optimal concentration of 150m M. This effect was due to stimulation of fumarate reductase activity as salt had little effect on NADH: decylubiquinone oxidoreductase (NADH dehydrogenase). The stimulation of fumarate reductase by salt at pH 6.0 was not due to removal of oxaloacetate from the enzyme. Kinetic parameters for several inhibitors were also measured. NADH dehydrogenase was inhibited by rotenone at a single site with a Ki of 1 μM. 2-Heptyl-4-hydroxyquinonline-N-oxide (HOQNO) inhibited NADH: fumarate reductase with a Ki of 0.006 μM, but NADH dehydrogenase exhibited two HOQNO inhibition constants of approximately 1 μM and 24 μM. Capsaicin and laurylgallate each inhibited NADH dehydrogenase by only 20% at 100 μM. NADH dehydrogenase gave Km values of 1 μM for NADH and 4 μM for reduced hypoxanthine adenine dinucleotide.