Copper uptake processes

Before dyeing with oxidation dyes, the furs are treated with the appropriate killing agents and then mordanted with metal salts. Iron, chromium, and copper salts, alone or in combination, are used for mordanting, and the uptake process requires several hours. Adjustment of the pH is effected with formic, acetic, or tartaric acid. The final dyeing process is carried out in paddles with the precursors and hydrogen peroxide until the actual dye lake is developed and adsorbed within the hair fiber. It takes quite a few hours at room temperature until the dyeing process is finished. 

If both MT-1 and HO-1 mRNA induction by heme-hemopexin involves a copper-redox enzyme in both heme transport (and consequent induction of HO-1 mRNA) and the signaling pathway for MT-1 expression, a plausible working model can be formulated by analogy with aspects of the yeast iron uptake processes and with redox reactions in transport (Figure 5-6). First, the ferric heme-iron bound to hemopexin can act as an electron acceptor, and reduction is proposed to be required for heme release. The ferrous heme and oxygen are substrates for an oxidase, possibly NADH-dependent, in the system for heme transport. Like ferrous iron, ferrous heme is more water soluble than ferric heme and thus more suitable as a transport intermediate between the heme-binding site on hemopexin and the next protein in the overall uptake process. The hemopexin system would also include a copper-redox protein in which the copper electrons would be available to produce Cu(I), either as the copper oxidase or for Cu(I) transport across the plasma membrane to cytosolic copper carrier proteins for incorporation into copper-requiring proteins [145]. The copper requirement for iron transport in yeast is detectable only under low levels of extracellular copper as occur in the serum-free experimental conditions often used. 

There are at least two pathways by which copper is transported across the cell membrane (DiDo-NATO and Sarkar 1997). Ceruloplasmin, the most abundant copper-protein in plasma, can contribute copper to cells (Hsie and Frieden 1975, Campbell et al. 1981, Dameron and Harris 1987, Mas and Sakar 1992, Saenko et al. 1994). Studies of ceruloplasmin-mediated copper transport in cells have shown that copper derived from ceruloplasmin enters the cell but the protein does not (Perci-VAL and Harris 1990). Stimulation of copper uptake by ascorbate and the inhibition of the process by cuprous chelators suggest that copper takes place in the form of Cu(I) rather than Cu(II) (Percival and Harris 1989, Harris 1991). 

This value indicates that the ion-exchange process is essentially irreversible, i.e. very favorable for the uptake of copper from solution. 

We described elsewhere the Hg(0) vapor sorption of commercial CuS [10]. The relative rate of Hg(0) uptake for commercial grade cuS is 12.8 mmoles/day compared with 70 mmoles/day for CTAB mediated CuS. The sorption properties of the particle-size-mediated synthesized covellite, CuS, is likewise reflective of a redox process that results in the formation of cinnabar, HgS, and the copper(I) sulfide chalcocite, CU2S, according to Reaction (1) ... 

Type IIA copper is defined as a monomeric copper site with a tetragonal ligand environment, exhibiting the spectroscopic features of conventional synthetic Cu(II) complexes. The coordination structure of the type IIA site is not remarkable from an inorganic point of view. What is noteworthy is the interaction between the copper ion and a prosthetic group or substrate. The electron uptake or activation of a substrate that occurs through this interaction plays an essential role in the catalytic cycle, yet the structural and mechanistic details are not certain. Therefore, the synthetic model approach may provide useful information for understanding the catalytic processes. 

Copper ion homeostasis in prokaryotes involves Cu ion efflux and sequestration. The proteins involved in these processes are regulated in their biosynthesis by the cellular Cu ion status. The best studied bacterial Cu metalloregulation system is found in the gram-positive bacterium Enterococcus hirae. Cellular Cu levels in this bacterium control the expression of two P-type ATPases critical for Cu homeostasis (Odermatt and Solioz, 1995). The CopA ATPase functions in Cu ion uptake, whereas the CopB ATPase is a Cu(I) efflux pump (Solioz and Odermatt, 1995). The biosynthesis of both ATPases is regulated by a Cu-responsive transcription factor, CopY (Harrison et al., 2000). In low ambient Cu levels Cop Y represses transcription of the two ATPase genes. On exposure to Cu(I), CopY dissociates from promoter/operator sites on DNA with a for Cu of 20 jlM (Strausak and Solioz, 1997). Transcription of copA and copB proceeds after dissociation of CuCopY. The only other metal ions that induce CopY dissociation from DNA in vitro are Ag(I) and Cd(II), although the in vivo activation of copA and copB is specihc to Cu salts. The CuCopY complex is dimeric with two Cu(I) ions binding per monomer (C. T. Dameron, personal communication). The structural basis for the Cu-induced dissociation of CopY is unknown. Curiously, CopY is also activated in Cu-dehcient cells, but the mechanism is distinct from the described Cu-induced dissociation from DNA (Wunderh-Ye and Solioz, 1999). 

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