Copper complexes transport

A lipophilic copper complex with neocuproine has been found to increase the toxicity of a trichlorophenol in bacteria, probably due to increased transport of Cu over the membrane [229],... 

Because Cu2+ is the most tightly bound metal ion in most chelating centers (Table 6-9), almost all of the copper present in living cells is complexed with proteins. Copper is transported in the blood by a 132-kDa, 1046-residue sky-blue glycoprotein called ceruloplasmin.471475-477 This one protein contains 3% of the total body copper. 

The electrons provided in the light reaction, however, may also be directly exported from the cells and used to reduce a variety of extracellular substrates. This electron export is effected by surface enzymes (called transplasmamembrane reductases) spanning the plasmamembrane from the inside surface to the outside. They transfer electrons from an internal electron donor [chiefly NADH and NADPH see Crane et al. (1985)] to an external electron acceptor. Direct reduction of extracellular compounds by transplasmamembrane electron transport proteins is prevalent in all cells thus far examined (Fig. 2.2). Although the function of this redox system is still subject to speculation, in phytoplankton it shows considerable activity, relative to other biochemical processes. A host of membrane-impermeable substrates, including ferricyanide, cytochrome c, and copper complexes, are reduced directly at the cells surface by electrons originating from within the cell. In phytoplankton, where the source of electrons is the light reactions of photosynthesis, the other half-redox reaction is the evolution of ()2 from H20. In heterotrophs, the electrons originate in the respiration of reduced substances. 

Cytochrome C Oxidase (Complex IV) Cytochrome c, after being reduced by the CoQH2-cytochrome c reductase complex, transports electrons, one at a time, to the cytochrome c oxidase complex (Figure 8-18). Within this complex, electrons are transferred, again one at a time, first to a pair of copper ions called Cu, then to cytochrome a, next to a... 

Figure 9.14 Effect of pH on copper coupled transport flux for three different complexing agents.20 (Membrane Celgard 2400. Feed 0.2% copper. Product 100 g/C H2S04).

Golgi apparatus, endoplasmic reticulum, and plasma membrane, and are responsible for copper transport. A mutation of this gene is responsible for Wilson s disease. Copper is poorly incorporated into the ceruloplasmin when translocase is defective. Metal ions are also sequestrated into lyso-somes, especially under conditions of copper overload (Mohan etal. 1995). The liver, which is the only true storage site that may be mobilized in the case of a negative copper balance, retains 20% of body copper. Muscles and brain account for 40% and 20%, respectively, but this copper is not available to assess in copper balance maintenance. A carrier-mediated facilitated diffusion system for uptake of copper complexes, amino acids and small peptides was identified in the rat hypothalamus (Harttler and Barnea 1988). Copper transport into the bile takes place in association with the biliary excretion of glutathione (Freedman etal. 1989). 

Thus, redox processes at the cell surface, possibly activated upon binding of heme-hemopexin to its receptor, generate cuprous ions which participate in HO-1 and MT-1 gene regulation by heme-hemopexin before heme catabolism. These are novel observations since they show for the first time that copper is involved in the biochemical and regulatory responses of cells to the transport and signaling activity of hemopexin. Since BCDS acts extracellularly, this chelator may remove copper from copper proteins or, as seems less likely, prevent the cellular uptake of Cu(I) itself or of Cu(I)-complex transport intermediates in solution if coordinated cycles of copper and heme uptake occur. 

If one compares the ratios of C2 Ci and CaiCi it appears that the system is in a state of rapid change for the first several hours equilibrium conditions are achieved virtually after about 3 hr for copper complexed with DOM and after about 5 hr for copper sorbed on SS. Subsequently, concentration changes are attributable entirely to the physical mechanisms of transport and dispersion. 

In mass-transfer-controlled systems in which extensive complexing or association takes place in the bulk phases, a proper mass transfer model must account for transport of all species. Otherwise, the transport model will not be consistent with a chemical model of phase equilibrium. For example. Fig. 8.4-4 indicates schematically the species concentration profiles established during the extraction of copper from ammonia-ammonium sulfate solution by a chelating agent such as LIX. In most such cases the reversible homogeneous reactions, like copper complexation by ammonia, will be fast and locally equilibrated. The method of Olandei can be applied in this case to compute individual species profiles and concentrations at the interfiice for use in an equilibrium or rate equation. This has been done in the rate analyses of several of the chloride and ammonia systems cited above. ... 

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