Chemistry and biochemistry of magnesium
Introduction
In this chapter we will describe the fundamental characteristics of the biochemistry of magnesium (Mg), which makes this ion essential to living organisms.
To begin with the description of its availability and molecular structure, characterized by an unique high ratio between hydrated and ionic radius, we will discuss its versatility in complexing a wide variety of macromolecules, from phospholipids to nucleic acids and proteins as well as small key molecules such as nucleotides. This peculiar capability to interact with different chemical structures certainly makes Mg the most versatile among intracellular cations, but such a versatility, together with the technical difficulties to trace it, has so far biased the exhaustive characterization of its multiple fundamental biologic roles.
Section snippets
Structure and distribution
Magnesium (Mg) is the fourth most abundant cation in living organisms (human body: Ca > K > Na > Mg), the second most abundant in the hydrosphere (sea water: Na = 450 mM, Mg and Cl ≅ 50 mM, Ca and K ≅ 10 mM), and the sixth most abundant in the lithosphere (O > Si > Al > Fe > Ca > Mg), basically in the form of dolomite (Alps), epsomite (England) and silicates such as olivine, an igneous rock and clays (Siegel, 1992). The biochemistry of Mg and other alkali metals and alkaline earth ions has been
Interaction with enzymes
In the intracellular environment, Mg is found in relatively high concentration (see Table 1), consequently the binding affinity of Mg for typical biologic ligands (low molecular weight and macromolecules) are low to moderate (102–105 M−1) (Huang and Cowan, 1994). In general, however, detailed crystallographic studies on ion–proteins relationships have been carried out for Ca rather than for Mg. Approximately 90% of intracellular Mg is bound to ribosomes or polynucleotides. Its biologic
Complexes with nucleic acid
Interactions with membranes, proteins and enzymes are not unique to Mg but are shared by other ions and especially Ca. An important feature of Mg biochemistry pertains its capability to form complexes with nucleic acids. The negatively charged ribose–phosphate backbone has an affinity for metal ions () which determines potentially facile interactions with a variety of metals. Other factors, like concentration and charge, will therefore establish a hierarchy between potential
Interaction with membranes
The walls of both prokaryotic and eukaryotic cells, including their internal structures and compartments, are composed of lipids, proteins, polysaccharides and phospholipids. Many surface polymers are polyanionic carboxylates or phosphates. Both Mg and Ca ions stabilize biologic membranes by charge neutralization after cross-linking the carboxylated and phosphorylated head groups of lipids. Chelating agents that bind these ions strongly (e.g. EDTA) will disrupt the membranes. Metal ion binding
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