Oxygen-18, nuclear activation

Mechanistic assays Various systems, e.g. cell lines, cell-free extracts, mitochondria, nuclear extracts GAP junction inhibition, oxidative stress measure, protein-binding activity, endocrine-disrupting activity, oxygen consumption, metabolite levels, etc. Mechanistic studies Non-genotoxic carcinogenicity, weight of evidence... 

There are only a few reports on the structures of active oxygen species formed on POMs. Recently, we have clarified some of the structures of the active oxygen species formed on POMs with nuclear magnetic resonance (NMR) spectroscopy, coldspray ionization mass spectrometry (CSI-MS), and single crystal X-ray structural analysis. In this section, we focus on the activation of H2O2 by the species (a)-(c) and present results from our recent studies. Some reaction mechanisms for H2O2-based oxidations by POMs are also described. 

Fig. 1 Immunoblots of acid extracts of nuclear preparations from mouse epidermal cells JB6 (clone 41) which had been treated with active oxygen produced by xanthine/xanthine oxidase (50 pg/ml xanthine plus 5 Xg/ml xanthine oxidase) for 30 min or 5 pg/ml MNNG for 20 min. The extracts were purified on a boronate affinity column and the proteins separated on 15% polyacrylamide gels (34). A polyclonal rabbit antibody against histone H3 (37) was used for the immunoblot and the blot was reacted with [i Sjj-iabeled donkey anti-rabbit IgG. Densitometer scannings are shown at the right side of the autoradiogram and were obtained with a Zeineh "soft laser" scanning densitometer.

Paraquat resistance in Conyza was traced to an elevated level of the Halliwell-Asada enzyme pathway responsible for the degradation of active oxygen species [36]. Resistance in Conyza is controlled by a single dominant nuclear gene that pleiotropically increases the level of the whole pathway [38]. 

Unfortunately, there are no convenient radioactive isotopes of oxygen. The stable isotopes are O (natural abundance being 99.76%), O (0.04%), and O (0.20%). At present the rarer isotopes can be purchased commercially in enrichments up to 99% and about 10% O, factors of 500 and 250, respectively, above their natural concentrations, and it has been shown that their use together with nuclear activations which make them radioactive can provide for their detection as if they were radiotracers C). The only difference is that they are made radioactive after a diffusion or reaction experiment rather than having been radioactive from the beginning. 

Depending on the non-metal element, its concentration and the matrix, the determination of the concentration of these elements requires more or less sophisticated analytical equipment. Classical analytical methods are only of limited possibilities techniques such as reducing fusion allow the determination of oxygen and nitrogen at concentration levels of a few g/g. To date, an accurate determination of concentrations below 1 Mg/g is only possible using nuclear activation methods such as e.g. photon- or charged particle activation. 

Nagayama et al. [36] studied a-sulfonation using nuclear magnetic resonance (NMR). They reported the presence of two intermediates. The first intermediate is the adduct of S03 to the carbonyl oxygen formed at low temperatures. In contrast to the mechanism of Stein et al., they did not propose a rearrangement of this intermediate but a second addition of S03 to the activated a-hydrogen to give the second intermediate. The reaction of the intermediate with sodium hydroxide can lead to the disodium salt if the neutralization is immediate or to the sodium a-sulfo fatty acid ester if the neutralization is delayed. 

IkB inhibitory protein kappa B lCAM-1 intercellular adhesion molecule 1 lL-1 interleukin-1 LDL low density lipoprotein MAPKs mitogen activated protein kinases MCP-1 macrophage chemotactic protein 1 M-CSF macrophage colony stimulating factor mmLDL minimally modified LDL NAC A-acetylcysteine NF-kB nuclear factor-kappa B oxLDL oxidised LDL PKC protein kinase C PMA phobol myristate acetate ROS reactive oxygen species TNF-a tumour necrosis factor alpha AM-1 vascular cell adhesion molecule 1... 

The release of iron from intracellular ferritin stores is thought to involve the reduction of Fe to Fe " (Funk et al., 1985) and one would expect this reduction to be fecilitated by the low oxygen tension, increased levels of reducing species and the low pH shown by nuclear magnetic resonance (NM to be as low as 6.9 after only 6 h of cold storage (Fuller et al., 1988). Exogenous redox-active quinones such as adriamycin have been shown to catalyse lipid peroxidation in the presence of ferritin under hypoxic conditions (Vile and Winterbourne, 1988), and lipid peroxidation is stimulated in micro-somes in the presence of purified ferritin and flavin... 

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