Although these findings cannot be extrapolated to humans, MX should be studied as a candidate risk factor in the possible association between consumption of chlorinated drinking water and cancer in humans.
In order to explore the observed association among mercury, atherosclerosis, and coronary heart disease, the effects of mercury, copper, and iron on the peroxidation of low-density lipoprotein (LDL) and on the enzymatic activities of glutathione peroxidase and myeloperoxidase were investigated in vitro. On the basis of our nuclear magnetic resonance (NMR) experiments, we conclude that mercury does not promote the direct nonenzymatic peroxidation of LDL, like copper and iron. In our enzyme measurements, mercury inhibited slightly myeloperoxidase, although not significantly in presence of LDL. Instead, inorganic mercury, but not methylmercury chloride, inhibited glutathione peroxidase effectively and copper even at 10 micromol/L, below physiological concentrations, doubled the inhibition rate. Copper and iron had no direct effect on glutathione peroxidase, but they both seem to activate production of HOCl by myeloperoxidase. We conclude here that, first, mercury and methylmercury do not promote direct lipid peroxidation, but that, second, a simultaneous exposure to high inorganic mercury, copper, and iron and low selenium concentrations can lead to a condition in which mercury promotes lipid peroxidations. This mechanism provides a plausible molecular-level explanation for the observed association between high body mercury content and atherosclerosis.
The 500 MHz proton spectra of monomeric bacteriochlorophyll a and chlorophyll a were recorded and assigned.The proton chemical shifts and proton-proton coupling constants were all determined except for the P-5 to P-15 phytyl side-chain protons. The conformational structures of the reduced rings and associated side-chains in these compounds were deduced from vicinal coupling constants. The reduced ring IV and the propionic ester side-chain in bacteriochlorophyll a and chlorophyll a have identical conformations which, in addition, are very similar to those reported previously for methyl pheophorbide a and pheophytin a. The reduced ring IV of bacteriochlorophyll a, which is attached to the phytyl side-chain, is more buckled than the other reduced ring (ring 11).
The 13C NMR spectra of C-10 epimeric chlorophylls a and a', pheophytins a and a', pyrochlorophyll a and pyropheophytin a have been recorded and assigned by chemical shift comparison, by long-range selective 'H decoupling experiments and by the examination of the fully coupled spectra. Various factors influencing the C chemical shifts of the chlorophyll derivatives, e.g. the coordination of magnesium to the chlorin nucleus, the effect of solvent and the steric strain at the periphery of the macrocycle, have been examined. The 13C NMR spectra of chlorophyll a measured in acetone-& and te&ahydrofuran-t-& were compared, and remarkable solvent effects on the 13C chemical shifts were observed. These effects were interpreted mostly in terms of specific chlorophyll-solvent interactions. Different electron donor and steric properties of acetone and THF were considered to cause conformational alterations in the macrocycle, induced by the Ligation of the solvent molecule(s) to the axial position(s) of the central magnesium atom of chlorophyll a. These results show that 13C NMR spectroscopy is a method of high information value for investigations of the unique electron donor acceptor (EDA) properties of the chlorophylls. The structural differences between the C-10 epimeric chlorophylls and pheophytins were examined in terms of the substituent chemical shift (SCS) parameters for the C-10 methoxycarbonyi group. The analysis showed that the change from the (10R) to the 10(!5) configuration induces conformational alterations in the whole macrocycle which are, however, most prominent in rings IV and V. Owing to the increased steric interaction (repulsion) between the bulky substituents at C-7 and C-10, the peripheral strain is larger in the (10s) form, and is relieved by more pronounced deviations of rings IV and V from the macrocyclic plane compared with the (10R) form. The examination of the SCS parameters also showed that the peripheral steric strain is dissipated to a larger extent over the entire macrocycle in the Mg-free derivatives. These results con* the previous conclusions based on 'H NMR and CD data. The possible function of chlorophyll a' in photosynthesis is briefly discussed.
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