Metal-complexes with Proteins

The ability of a metal ion to increase the rate of hydrolysis of a peptide has enormous implications in biology, and many studies have centred upon the interactions and reactions of metal complexes with proteins. However, hydrolysis is not the only reaction of this type which may be activated by chelation to a metal ion, and chelated esters are prone to attack by any reasonably strong nucleophile. For example, amides are readily prepared upon reaction of a co-ordinated amino acid ester with a nucleophilic amine (Fig. 3-11). In this case, the product is usually, but not always, the neutral chelated amide rather than a depro-tonated species. 

Top-down proteomics However, the typical analytical approaches to proteomics usually ignore the existence of metal complexes with proteins. The information on the metal-protein interactions is either lost during ionization (e.g. MALDI), on the procedures of sample preparation (because of denaturation), or simply not acquired because of the inadequate ionization efficiency, and, consequently, insufficient sensitivity. ... 

The entirety of metal complexes with proteins in 31,34 a sample. Note that this term was originally used in a narrower sense and concerned the proteins with enz5matic functions only... 

These examples are part of a broader design scheme to combine catalytic metal complexes with a protein as chiral scaffold to obtain a hybrid catalyst combining the catalytic potential of the metal complex with the enantioselectivity and evolvability of the protein host [11]. One of the first examples of such systems combined a biotinylated rhodium complex with avidin to obtain an enantioselective hydrogenation catalyst [28]. Most significantly, it has been shovm that mutation-based improvements of enantioselectivity are possible in these hybrid catalysts as for enzymes (Figure 3.7) [29]. 

Anthocyanins can form complexes with metal ions such as tin, iron and aluminium. The formation of a complex, as expected, alters the colour, usually from red to blue. Complex formation can be minimised by adding a chelating agent such as citrate ions. Another problem with anthocyanins is the formation of complexes with proteins. This can lead to precipitation in extreme cases. This problem is normally minimised by careful selection of the anthocyanin. 

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. 

Our knowledge concerning soluble metal complexes with sulfide ions as ligands has increased considerably during the last two decades and this kind of Compound is still of topical interest. Some of the reasons for this are the development of a very flexible and fascinating structural chemistry of multinuclear metal-sulfur complexes, the fact that the active sites of some electron transfer proteins contain metal ions and labile sulfur,41,42 and also the relation of metal-sulfur cluster compounds to some heterogeneous catalysts. In addition, apart from the numerous binary and ternary sulfides which occur in nature, we have at our disposal a rich solid state chemistry of metal sulfides, which has been reviewed elsewhere and will be excluded here.43"17... 

The heavy metal ions form complexes with proteins, in which carboxylic acid (-COOH), amine (-NH2), and thiol (-SH) groups are involved. These modified biological molecules lose their ability to function properly and... 

Karadjova and coworkers [90] in a detailed and comprehensive investigation established a scheme for fractionation of wine components and Cu, Fe, and Zn determination in the different fractions. Like Fe, the other two metals may analogously exist in wines as free ions, as complexes with organic acids and as complexes with proteins, polyphenols and polysaccharides. The resin XAD-8 was used for the separation of wine polyphenols. Dowex ion exchange resins were used for the separation of cationic and anionic species of metals that were subsequently quantified off-line in Bulgarian and Macedonian wines by FAAS or ET-AAS (depending on their concentration levels). 

ORD spectra of copper complexes with a variety of proteins and peptides give conformational as well as quantitative information on the metal binding (9, 10, 35). This method also has been successfully applied to study metal complexes with nucleotides (53, 70). 

TCs are well documented to bind various metal ions, including alkaline earth metals, Al(ni) and transition metals VO(II), Cr(III), Mn(II), Fe(II/III), Co(II), Ni(II), Cu(II) and Zn(II) . TC can form 2 1 TC-metal complexes with transition metal ions in non-aqueous solution, in which the metal is bound at the 2-amido and 3-enolate chelating sites . TCs are present in plasma mainly in the Ca(II)-bound form or Mg(n)-bound form to a lesser extent, when they are not bound to proteins such as serum albumin. Thus, the bioavailability of TCs should be dependent upon the physical and biochemical properties of their metal complexes instead of their metal-free form. 

Silver, one of the native metals and second only to gold in its stability amongst the metals of antiquity, has provided several therapeutic agents which have been employed since the beginning of recorded history. These agents range from the metal itself, its salts and complexes with proteins and other macromolecules to the latest, AgSD. 

J). Bread components other than phytate were examined for their ability to bind metals. Fiber, protein and starch of wheat formed stable complexes with zinc and calcium, and later iron was found to share this behavior. The metals combined with protein or wheat starch, however, were released during digestion with peptidases and amylases (2,1)5). By contrast dietary fiber, being resistant to digestive secretions, retained bound metal intact. Removal of phytate, which had in the past been held to be the main source of metal complexation by bread, did not decrease but tended to enhance the binding of the metal (J2.). Further doubt about the role of... 

METALS The important metals in living organisms fall into two classes the transition metals (e.g., Fe2+ and Cu2+) and the alkali and alkaline earth metals (e.g., Na+, K+, Mg2+, and Ca2+). Because of their electronic structures, the transition metals are most often involved in catalysis. Although they have important functions in living organisms, the alkali and alkaline earth metals are only rarely found in tight complexes with proteins. This discussion is therefore concerned with the properties of the transition metals. 

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