Copper biomolecules

Turecek, F. Copper-biomolecule complexes in the gas phase. The ternary way. Mass Spectrom. Rev. 2007,26, 563-582. 

Similarly to dyes, some fluorescent proteins can be incorporated into polymeric beads to be used as an alternative for ion sensing. For example, a reporter protein (composed of a phosphate-binding protein, a FRET donor (cyan fluorescent protein) and a FRET acceptor (yellow fluorescent protein)) was incorporated into polyacrylamide nanobeads by Sun et al. [46]. FRET was inhibited upon binding of phosphate. Kopelman and co-workers [47] used a similar approach to design a nanosensor for copper ions. They have found that fluorescence of red fluorescent protein DsRed (commonly used as a label) is reversibly quenched by Cu2+ and Cu+. Both DsRed and Alexa Fluor 488 (used as a reference) were entrapped into polyacrylamide nanobeads. Typically, up to 2 ppb of copper ions can be reliably measured. It should be mentioned, that in contrast to much more robust dyes, mild conditions upon polymerization and purification are very important for immobilization of the biomolecule to avoid degradation. 

These examples illustrate that biomolecules may act as catalysts in soils to alter the structure of organic contaminants. The exact nature of the reaction may be modified by interaction of the biocatalyst with soil colloids. It is also possible that the catalytic reaction requires a specific mineral-biomolecule combination. Mortland (1984) demonstrated that py ridoxal-5 -phosphate (PLP) catalyzes glutamic acid deamination at 20 °C in the presence of copper-substituted smectite. The proposed pathway for deamination involved formation ofa Schiff base between PLP and glutamic acid, followed by complexation with Cu2+ on the clay surface. Substituted Cu2+ stabilized the Schiff base by chelation of the carboxylate, imine nitrogen, and the phenolic oxygen. In this case, catalysis required combination of the biomolecule with a specific metal-substituted clay. 

The role of the transition elements in living systems is equally important. Iron is present in biomolecules such as hemoglobin, which transports oxygen from our lungs to other parts of the body. Cobalt is an essential component of vitamin B12. Nickel, copper, and zinc are vital constituents of many enzymes, the large protein molecules that catalyze biochemical reactions. 

A number of investigations of metal-containing biomolecules are described in this chapter. The elements include aluminium, arsenic, cadmium, copper, gold, lead, platinum and zinc. 

Some metal- (especially copper) complexes catalyse the dismutation of superoxide at rates that compare favourably with catalysis by superoxide dismutase. One could therefore argue that the presence of such complexes in vivo might be beneficial. There are, however, additional considerations (1) such metal complexes may also reduce hydrogen peroxide, which could result in the formation of hydroxyl radicals, and (2) it is extremely likely that the metal will be displaced from its ligands (even when those ligands are present in excess), and becomes bound to a biomolecule, thereby becoming less active as a superoxide dismutase mimic. As an example, copper binds well to DNA and catalyses the formation of hydroxyl radicals in the presence of hydrogen peroxide and ascorbate [30],... 

There are a number of enzymes that catalyse the dismutation of superoxide in vivo, viz. the superoxide dismutases [50,51], They are metalloproteins which contain copper, zinc, manganese or iron as the prosthetic group. The enzyme catalase exists in vivo to degrade hydrogen peroxide within cells to form water and oxygen [43]. As stated earlier, there are barely detectable amounts of these two enzymes in the synovial fluid of arthritic patients and hence both superoxide radicals and hydrogen peroxide are potential mediators of damage to the biomolecules of the synovial fluid. 

From the known chemical properties of superoxide free radicals and hydrogen peroxide, it is unlikely that these two species will react directly with the range of biomolecules found in synovial fluid. It is more likely, particularly for superoxide radicals, that they will instead participate in redox reactions with complexes of metal ions such as iron and copper, although reaction with phenolic compounds cannot be excluded. It has been proposed therefore that synovial fluid, in particular hyaluronic acid, can be degraded in vivo through an iron-catalysed Haber-Weiss reaction. 

Excess copper is toxic to cells. On one hand, copper ions can avidly bind to biomolecules by ligand interaction with cysteines or by binding to histidine-rich regions. Copper ions could also be incorporated into proteins instead of zinc or other metal ions during biosynthesis. On the other hand, copper ions can form radicals by a Fenton-type reaction as shown in Eq. (1) ... 

This reaction generates reactive hydroxyl radicals that can damage biomolecules. However, cellular hydrogen peroxide is rapidly removed by catalase and concentrations are very low, usually in the submicromolar concentration range. A Fenton-type reaction may therefore not be the primary cause of copper toxicity (Kaim and Rail, 1996). An alternative route of copper-induced cell damage is the depletion of sulfhydryls by redox cychng as described in reactions (2) and (3) ... 

Copper proteins can fill quite different biological roles. In each case, the function is determined by the three-dimensional structure of the biomolecule as well as by the coordination geometry of the metal site, which in turn determines the electronic structure of the metal ion(s) (Bertini et al., 1993c, 1994a Holm et al., 1996 Solomon et al., 1992). 

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