Magnesium Ions

Magnesium (Mg), the second most abundant soft tissue intracellular cation in vertebrates, is an essential nutrient for all organisms. Because of its small ionic radius and relatively large charge, Mg²⁺ functions within living cells primarily as a reversible chelator, forming relatively stable complexes, particularly with phosphoryl and carbonyl groups. In so doing, it activates or inhibits enzyme substrates involved in the metabolism of carbohydrates and lipids; is an essential cofactor in the synthesis of proteins and nucleic acids; facilitates the transfer of high-energy phosphate bonds; combines directly with certain enzymes and membrane-bound transport systems; forms stabilizing complexes with ribosomes, phospholipids, and components of the cytoskeleton; and promotes cellular cohesion. (see Aikawa, 1971; Guenther, 1981; Wacker, 1980). Although most of its biochemical functions have been worked out in vitro or in vivo in isolated enzyme and other biologic systems and in cells from nonnervous tissues, there is every reason to believe Mg²⁺ functions similarly in the cells in the nervous system. For example, CNS hexokinase, a critical enzme in aerobic metabolism of carbohydrates, probably requires Mg²⁺ for allosteric activation when the concentration of ATP falls below that of free Mg²⁺ in the cytosol (Lustyil, and Nagy, 1985).