Copper, protein bound

As we will discuss later, in Chapter 8, free copper levels are extremely low within cells because the copper is bound to a family of metallochaperones, which are subsequently involved in the incorporation of copper into copper-containing proteins. The mechanism proposed for copper insertion into the Cu/Zn superoxide dismutase, SOD1, is presented in Figure 3.9. The copper chaperone, CCS, acquires copper as Cu+ from a copper transporter and then docks with the reduced dithiol form of SOD1 (Steps I and II) to give a docked... 

When copper is bound to one sulfur atom of a cysteine and two nitrogens of two histidines in an essentially tetrahedrally distorted - trigonal ligand environment (type I copper proteins), the excited levels are low in energy, and the values are reduced to about 5 x 10 ° s (29). Examples are blue copper proteins, like ceruloplasmin and azurin, and copper(II) substituted liver alcohol dehydrogenase (30-32). 

Copper-containing amine oxidases (non-blue copper proteins) catalyze the oxidative deamination of primary amines to the corresponding aldehydes with the release of ammonia and concomitant reduction of oxygen to hydrogen peroxide. They typically use a quinone redox cofactor [topaquinone (TPQ)], which is bound covalently in the active site, and are thought to form a Cu(I)-TPQ semi-quinone radical intermediate during the redox reaction [13]. 

Table I lists isomorphous replacements for various metalloproteins. Consider zinc enzymes, most of which contain the metal ion firmly bound. The diamagnetic, colorless zinc atom contributes very little to those physical properties that can be used to study the enzymes. Thus it has become conventional to replace this metal by a different metal that has the required physical properties (see below) and as far as is possible maintains the same activity. Although this aim may be achieved to a high degree of approximation [e.g., replacement of zinc by cobalt(II)], no such replacement is ever exact. This stresses the extreme degree of biological specificity. The action of an enzyme depends precisely on the exact metal it uses, stressing again the peculiarity of biological action associated with the idiosyncratic nature of active sites. (The entatic state of the metal ion is an essential part of this peculiarity.) Despite this specificity, the replacement method has provided a wealth of information about proteins that could not have been obtained by other methods. Clearly, there will often be a compromise in the choice of replacement. Even isomorphous replacement that should retain structure will not necessarily retain activity at all. However, it has become clear that substitutions can be made for structural studies where the substituted protein is inactive (e.g., in the copper proteins and the iron-sulfur proteins). It is also possible to substitute into metal coenzymes. Many studies have been reported of the...

The type-1 blue copper proteins act as electron carriers azurin, plastocyanin, stellacyanin, umecyanin e.g. They are characterized by a rather strong LMCT (ligand to metal charge transfer) band near 600 nm and by small hyperline coupling constants A in EPR. Copper is bound to two imidazole groups of histidine and to two... 

The other way to study the "conductivity of protein molecules towards electron tunneling is to investigate the quenching of luminescence of electron-excited simple molecules by redox sites of proteins [95,96]. Experiments of this sort on reduced blue copper proteins have involved electron-excited Ru(II)(bpy)3, Cr(III)(phen)3, and Co(III)(phen)3 as oxidants. The kinetics of these reactions exhibit saturation at protein concentrations of 10 3 M, suggesting that, at high protein concentrations, the excited reagent is bound to reduced protein in an electron transfer precursor complex. Extensive data have been obtained for the reaction of reduced bean plastocyanin Pl(Cu(I)) with Cr(III)(phen)3. To analyze quenching experimental data, a mechanistic model that includes both 1 1 and 2 1 [Pl(Cu(I))/ Cr(III)(phen)3] complexes was considered [96]... 

Plasma levels of some hormones (thyroid and steroid hormones), vitamins (vitamin D metabolites), ions (iron, copper, and zinc) and drugs maybe low in nephrotic subjects because of the low levels of protein-bound ligands (K11), as binding proteins are lost into the urine. Ligands also may be lost in the urine together with their... 

Chemically, human hair contains approximately 85 percent protein, 7 percent water, 3 percent lipid, 4.7 percent protein-bound sulfur (as cystine), and low concentrations of trace minerals (e.g., iron, zinc, copper). The phosphorus content is approximately 80 milligrams per 100 grams (0.003 ounces per 3.5 ounces) of hair. Hair is normally associated with sebum and exocrine secretions from skin glands that confer greasiness but influence its water content and mechanical and physical properties. 

The plastocyanins are blue copper proteins found in the chloroplasts of higher plants and algae where they mediate electron transport between cytochrome f and P-700 (Barber, 1983 Haehnel, 1984, 1986 Cramer etal., 1985 Sykes, 1985 Andersen et al., 1987). Plastocyanins each contain one copper bound by a single polypeptide chain of molecular weight around 10500 (Sykes, 1985). The spectroscopic properties of the copper are those of a typical blue site. The properties of the plastocyanins have been the subject of detailed reviews (Sykes, 1985 Haehnel, 1986 Chapman, 1991). 

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