Amino Acids interactions with metal ions

Zubay, G., and P. Doty Nucleic acid interactions with metal ions and amino acids. Biochim. Biophys. Acta 29, 47 (1958). 

In a tight transition state, negative charge on the phosphoryl group increases. Thus, interactions with metal ions or positively charged amino acids, which are found at the active sites of enzymes that catalyze phosphoryl transfers, would intuitively favor an associative mechanism. 

Non-isoprene mechanisms and compounds responsible for gel formation have been intensely studied. Prior to the recent proposals made by Tanaka et so-called abnormal compounds were incriminated in the interactions responsible for gel. Those compounds (aldehydes/" epoxyj esters ) were linked to the polyisoprene chain and reacted with some non-isoprene compounds (amino acids or proteins, metal ions ). 

Leather is a complicated material but contains much protein it is always a good ligand, because it contains peptide linkages, from which either oxygen or nitrogen can donate electrons to a metal ion, forming a coordinate bond, and in which the many functional groups of the side chains of the amino acids may also interact with metal ions (as shown by the atoms underlined in structure 2). 

Surfactant effects on adsorption of herbicides on to soil have been investigated and suggested to be a factor to be considered in the overall effect of surfactant on toxicity towards the plant. The degradation, mobility and uptake of one such compound, picloram [4-amino-3,5,6-trichloropicolinic acid] (pK = 3.4) is affected by adsorption-desorption processes in solids. Picloram adsorption on to soils at pH 5 was reduced by 1 % anionic surfactant [284]. The mechanism involved in picloram adsorption included protonation of the molecule, metal-ion bridging and interaction with metal ions. Picloram adsorption was enhanced by cationic surfactants, suggesting that hydrophobic adsorption of the cationic monomers on to the soil provides a cationic surface for interaction of the anionic picloram. Different soils with different pH values resulted in some variations in these effects which are presented in Table 10.29. 

The native conformation of proteins is stabilized by a number of different interactions. Among these, only the disulfide bonds (B) represent covalent bonds. Hydrogen bonds, which can form inside secondary structures, as well as between more distant residues, are involved in all proteins (see p. 6). Many proteins are also stabilized by complex formation with metal ions (see pp. 76, 342, and 378, for example). The hydrophobic effect is particularly important for protein stability. In globular proteins, most hydrophobic amino acid residues are arranged in the interior of the structure in the native conformation, while the polar amino acids are mainly found on the surface (see pp. 28, 76). 

The rates of hydrolysis of amino acid esters or amides are often accelerated a million times or so by the addition of simple metal salts. Salts of nickel(n), copper(n), zinc(n) and cobalt(m) have proved to be particularly effective for this. The last ion is non-labile and reactions are sufficiently slow to allow both detailed mechanistic studies and the isolation of intermediates, whereas in the case of the other ions ligand exchange processes are sufficiently rapid that numerous solution species are often present. Over the past thirty years the interactions of metal ions with amino acid derivatives have been investigated intensively, and the interested reader is referred to the suggestions for further reading at the end of the book for more comprehensive treatments of this interesting and important area. 

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. 

Figure 8.2 Variants of affinity chromatography, (a) biospecific AC (b) metal chelate chrom. (c) charge transfer adsorption chrom. (d) hydrophobic interaction chrom. and (e) covalent chrom. (chemisorption). Abbreviations E = enzyme, L = amino acid group, me = meted ion, Rw = electron - withdrawing substituent, Rr = electron -donating substituent taken from ref. (47) with permission.

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