![]() Structural Zn 2+ sites have important implications for the functioning of metalloproteins. In some structural sites, it can be found either as a single metal ion or as part of a cluster of two or more ions, being coordinated only by amino acid residues with no bound solvent molecules. The Zn 2+ plays an important role in the structure of proteins and cell membranes. The total Zn 2+ concentration in eukaryotic cells was reported to be in the high micromolar range, with a concentration around 200 mM. Physiologically, approximately 98% of the total Zn 2+ in an organism is found within the cell (40% in the nucleus and 50% in cytoplasm, organelles, and specialized vesicles), while the remaining is localized in the cell membrane. These facts indicate various roles of ions in structural stabilization of proteins, nucleic acid, and cell membranes.Īmong the group II chemical elements, Zn 2+ is the second most abundant metal ion, after the iron, in all biological systems including microorganisms, plants, and animals. It was shown that approximately 90% of intracellular Mg 2+ is bound to ribosomes or polynucleotides. Since the intracellular concentrations of Na + and Ca 2+ are low, the metal binding chemistry of the nucleic acids in vivo is dominated by the more abundant K + and Mg 2+, but Mg 2+ is found more frequently in binding to nucleic acids due to its double positive charge in comparison to K +. The same pattern holds for K + hence, both Mg 2+ and K + are typically referred to as intracellular cations. Unlike Na +, Ca 2+ and Cl −, which accumulate in extracellular milieu, Mg 2+ is at least one order of magnitude more abundant inside the cell than in extracellular milieu. ![]() The Mg 2+ is an integral component of chlorophyll and serves an essential function for photosynthesis as well. Thus about 60–65% of total Mg 2+ are found in bone, about 35% in tissue compartments, and only about 1–2% in extracellular fluid including the plasma. The Mg 2+ is the fourth most abundant element in vertebrates and the most abundant divalent cation within cells. Thus, Na +, K + and Mg 2+ are the major components of bodily fluids and the cytoplasma of the cells. ![]() Therefore determining ions position in macromolecules is essential for understanding their structural and functional properties.įour ions, Na +, K +, Mg 2+ and Ca 2+, are widely distributed in all living organisms. Metal ions are crucial for stabilizing proteins structure and hence, affect their function. Statistical studies indicate that 70% of all enzymes bind metal ions. Most of these chemical elements are required for enzymatic activities, structural integrity, or simply provide screening of the electrostatic interactions in the water phase. There are seventeen additional chemical elements such as V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, B, Si, Se, F, I, As, Br and Sn, termed group II, which are found in some living organisms but not in all. Together with seven other elements (Na +, K +, Ca 2+, Mg 2+, P 3−, S 2− and Cl −), termed group I, they are considered to be essential or to be the basic components of organic structure. ![]() Four of them (O 2−, H +, C and N 3−) constitute 99.9 % of total number of atoms present in living organisms. The analysis indicates that eleven chemical elements appear to be predominant in all biological systems. Since these characteristics differ among the cellular compartments, the non-specific ion binding must be investigated with respect to the sub-cellular localization of the corresponding macromolecule.Īmong all chemical elements in the periodic table, biological systems utilize only a few. In addition, the binding and the residential time of non-specifically bound ions are very much sensitive to the environmental factors in the cells, specifically to the local pH and ion concentration. It is indicated that specifically bound ions are relatively easier to be revealed while non-specifically associated ions are difficult to predict. Furthermore, the experimental techniques to identify ion positions and computational methods to predict ion binding are reviewed and their advantages compared. This review outlines the differences between specific and non-specific ion binding in terms of the function and stability of the corresponding macromolecules. The ions can bind to the macromolecules either specifically or non-specifically, or can simply to be a part of the water phase providing physiological gradient across various membranes. Biological macromolecules carry out their functions in water and in the presence of ions.
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