Other Metal-containing Biomolecules

The one-carbon transfer reaction (left) facilitated by the octahedral cobalt(III) complex Vitamin Bi2 (right) as coenzyme. Carbon-cobalt bonding of the substrate is involved in the mechanism, at the site designated by the R-group in the complex. 

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It is well known that a great variety of biomolecules exist where metals and metalloids are bound to proteins and peptides, coordinated by nucleic acids or complexed by polysaccharides and small organic ligands such as organic acids.55 Most proteins contain amino acids with covalently bonded heteroelements such as sulphur, selenium, phosphorus or iodine.51 Several reviews have been published on the development of mass spectrometric techniques for bioanalysis in metal-lomics , which integrate work on metalloproteins, metalloenzymes and other metal containing biomolecules.1 51 53 54 56-59 The authors consider trace metals, metalloids, P and S (so-called... 

In the 2002 international symposium on bio-trace elements held in Japan, Haraguchi proposed the concept and term of metallomics as a new scientific field to integrate the research fields related to biometals. The concept was further elucidated in his successive publication, in which metallomics was defined as bio-trace element science, and metalloproteins, metalloenzymes and other metal-containing biomolecules were defined as metallomes in a similar manner to genomes in genomics as well as proteomes in proteomics. Subsequently, the term metallomics has been used as the name for the study of metallomes. Szpunar defined metallomics as ... comprehensive analysis of the entirety of metal and metalloid species within a cell or tissue type . ... 

The following protocol assumes that the user has at least two pure proteins (or biomolecules) of known sequences, which are able to interact specifically in solution. One of the two proteins (the prey) is end labeled with a fusion tag or another detectable component and the other protein contains at least one thiol group. All buffers and reagents used in this protocol should be of high purity and contain a very low metal content to prevent nonspecific cleavage reactions. 

Displacing the Essential Metal Ion in Biomolecules. It is estimated that approximately one third of all enzymes require metal as a cofactor or as a structural component. Those that involve metals as a structural component do so either for catalytic capability, for redox potential, or to confer steric arrangements necessary to protein function. Metals can cause toxicity via substitution reactions in which the native, essential metal is displaced/replaced by another metal. In some cases, the enzyme can still function after such a displacement reaction. More often, however, enzyme function is diminished or completely abolished. For example, Cd can substitute for Zn in the protein famesyl protein transferase, an important enzyme in adding famesyl groups to proteins such as Ras. In this case, Cd diminishes the activity of the protein by 50%. Pb can substitute for Zn in 8-aminolevulinic acid dehydratase (ALAD), and it causes inhibition in vivo and in vitro. ALAD contains eight subunits, each of which requires Zn. Another classic example of metal ions substituting for other metal ions is Pb substitution for Ca in bones. 

On the other hand, as biological molecules become larger their tendency to be associated with water molecules, metal ions, and other materials increases. Crystalline proteins, for example, routinely contain 27-65 % of the solvent used for their crystallisation 183). Such associated materials may be difficult to locate by crystallography and it may become a question of terminology whether such molecules should be regarded as inclusion complexes, non-specific aggregates, or merely contaminated biomolecules. 

Dendrimers can be used to effectively coat and passivate fluorescent quantum dots to make biocompatible surfaces for coupling proteins or other biomolecules. In addition, the ability of dendrimers to contain guest molecules within their three-dimensional structure also has led to the creation of dendrimer-metal nanoclusters having fluorescent properties. In both applications, dendrimers are used to envelop metal or semiconductor nanoparticles that possess fluorescent properties useful for biological detection. 

Polysaccharides are used as structural units and as stored energy sources. Proteins are used to construct muscle and enzymes that also contain metals such as zinc, manganese, and iron. There are many other important biomolecules present at lower concentrations such as DNA and RNA, which are also released into the soil solution. All can be the source of smaller molecules in the soil solution. 

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