Magnesium biochemical function

Iron, the central element in oxygen transport and utilization, is discussed in Chapter 29. Iodine, a constituent of thyroid hormones, is discussed in Chapter 33. Sodium, potassium, and chloride, which are important for maintaining proper osmolality and ionic strength and for generating the electrical membrane potential, are discussed in Chapter 39. Most of this chapter is devoted to the metabolism of calcium and phosphorus because of their importance in the skeleton and other body systems. Because of its chemical and biological relationship to calcium, magnesium is also covered. The trace elements are surveyed with emphasis on those for which a biochemical function is known. 

Magnesium ion is essential for normal Ca " and K" metaboHsm. In acute experimental magnesium deficiency in humans, hypocalcemia occurs despite adequate calcium intake and absorption and despite normal renal and parathyroid functions. Negative K" balance is also observed. AH biochemical and clinical abnormaHties disappear upon restoration of adequate amounts of magnesium to the diet (64). 

Magnesium is the second most abundant intracellular cation. Magnesium serves as an essential cofactor for numerous enzymes and in many biochemical reactions, including reactions involving adenosine triphosphate (ATP).17 Magnesium disorders can be multifactorial and can be related to renal function, disease... 

This chapter has emphasized again the advantage of having A, G ° for an enzyme-catalyzed reaction as a function of temperature, pH, and ionic strength. If magnesium ions or other ions are bound by reactants, the free concentrations of more ions can be included as independent variables. This chapter has also emphasized the value of calorimetric data. More standard transformed enthalpies of reaction need to be measured so that temperature effeets can be calculated for more reactions. The database can also be extended by use of reliable estimation methods based on species properties. This may be especially useful with larger biochemical reactants where reactive sites are nearly independent. 

Lithium might be expected to affect bone structure and function because of its chemical similarity to magnesium and calcium. In elderly lithium-treated patients and in animal experiments using weanling and mature rats, lithium was shown to accumulate in bone (204). Further biochemical studies showed no evidence of resulting bone defects (205, 206). Bone density measurements on mature rat bone, and on hand radiographs in lithium patients, failed to show any significant differences attributable to lithium (206). 

PTH is biochemically synthesized as a prohormone, which differs from PTH by the fact that it has six additional residues at the ami-no-terminus. The exact function of the prohormone sequence is unclear but it has been hypothesized that the production of PTH as a prohormone is important for the efficient packaging of the hormone. Although calcium ion concentrations in blood appear to play a significant role in the regulation of PTH, other agents such as magnesium, epinephrine, and dopamine also play a role in regulating PTH secretions in vivo. 

Magnesium is an element that has numerous functions in biochemical and physiological pathways. The animal body contains about 0.05% Mg (Rook and Storry, 1962), of which about 70% is contained in the skeleton with... 

Functions of Magnesium In plants, the main physiological role of magnesium is its contribution to the function of chlorophyll, though many other biochemical pathways have a need for magnesium. 

Like calcium, magnesium is involved in numerous functions in living organisms concerning the activity of different enzymes as well as the neuromuscular activity. By this magnesium deficiency influences many biochemical processes followed by significant clinical symptoms, especially neuromuscular exutibility, heart dysrhythmia, and increased risk to cardiovascular... 

The widespread importance of trace metal ion complexing in biochemical systems has become apparent from recent research. Iron and magnesium in hemoglobin and chlorophyll are well known, while the need and functions of Co, Zn, Mn, Cr, Mo, and others are under active investigation. Knowledge of possible competing equilibria is required for understanding of reactions of these metal ions. 

---