ATPase magnesium ions

Chapter 6 discussed Group II metal ions in biomolecules, concentrating on magnesium ions in catalytic RNA and on two calcium-containing biomolecules calmodulin and Ca -ATPase. Readers interested in the evolutionary aspects of catalytic RNA as a precursor to the DNA-based life forms that exist in the present time could begin by consulting the publications fisted in... 

Fig. 7. Influence of magnesium ion concentration on ATPase activity of thrombosthenin at low (left) and high ionic strength (right). ATP, 10 Af temperature, 20°C. From Beltex-Galland and Luscher (1961).

Calcium ions (Ca ) are important for the mediation of hepatic injury. Cytosolic free calcium is maintained at relatively low concentrations compared to the extracellular levels. The majority of intracellular calcium is sequestered within the mitochondria and endoplasmic reticulum. Membrane associated calcium and magnesium ATPases are responsible for maintaining the calcium gradient (Farrell et ah, 1990). Significant and persistent increases in the intracellular calcium result from nonspecific increases in permeability of the plasma membrane, mitochondrial membranes, and membranes of the smooth endoplasmic reticulum. Calcium pumps in the mitochondrial membrane require NADPH, thus depletion of available NADPH can cause calcium release from mitochondria (Cullen, 2005). 

With ATP and Mg++ ions, precipitates of these extra< ts will show superprecipitation, i.e., a comparatively slow contraction, which is abolished by the addition of Salyrgan. ATP sensitivity is about 70 % and the ATPase activity amounts to 0.002-0.003 mole P, per milligram of protein per minute (cf. Table IV). This activity varies with the ionic strength and with the magnesium concentration it too is inhibited by Salyrgan. 

The question for the nutritionist and clinician is Which Mg-dependent function is most sensitive to depletion of the body s magnesium and to hypomagnesemia The answer is probably ion transport systems, such as the calcium pump and Np,K-ATPase. The impaired activity of these ion pumps is likely to be responsible for the neuromuscular problems that present with an Mg deficiency. The defects would involve a difficulty in maintaining the normal movements of calcium, sodium, and potassium ions required for nerve conduction and muscle contraction,... 

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