Histone-produced magnesium extrusion from mitochondria and magnesium binding to histone.

Histone (60 microgram/mg mit. protein) extrudes Mg2+ from mitochondria by 30% with the utilization of endogenous substrates; in the presence of rotenone extrusion drops to about 18%. Dinitrophenol and ADP prevent this effect of histone. Mg2+ extrusion produced by histone depends on histone concentration being at a maximum (100% extrusion) at 107 microgram histone/mit. protein. It was found also that histone alone binds Mg2+ (1.6 nmol Mg2+/microgram histone).     

Post-cholecystectomy syndrome and magnesium deficit.

The serum level of magnesium and calcium was systematically measured in patients with gallstones before and after cholecystectomy. It was found that 60 percent of the operated patients suffered of different digestive syndromes in association with magnesium deficiency, while 40 percent of patients had the same complaints in association of magnesium and calcium deficiency. When magnesium and/or magnesium plus calcium was supplemented these syndromes could be decreased significantly. In the latter case, an optimal ratio of magnesium/calcium is needed in the supplementary therapy.     

Intracellular magnesium and magnesium buffering

The development of new techniques for measuring intracellular free Mg²⁺ during the 1980s has provided investigators with the tools needed to produce new insights into the regulation of cellular magnesium. Within the limits of this technology, it appears that all mammalian cells maintain free cytosolic Mg²⁺ levels within the fairly narrow range of 0.25–1 mM. While transport mechanisms and sequestration within cellular organelles will contribute to this regulation, it is binding of Mg²⁺ to an as yet poorly defined system of buffers that is largely responsible for determining the set point of this regulation. The lack of an adequately Mg²⁺-selective ionophore remains an impediment to progress in this area.     

The binding of polyamines and magnesium to DNA.

1. The binding of spermine and Mg2+ to DNA has been investigated using the dye arsenazo III to measure unbound cations. 2. The apparent dissociation constant, Kd, of DNA for spermine has been found to be 7.4 +/- 3.9 x 10(-8) M and that for Mg2+, 6.5 +/- 3.3 x 10(-7) M. 3. Binding of spermine in the presence of 1 mM Mg2+ has been shown to have a Kd of about 4 x 10(-6) M. 4. Magnesium ion (2 mM) halves the concentration of spermine needed to cause DNA aggregation. 5. Spermidine binds to DNA with a similar affinity to spermine but 3,3'-iminobispropylamine and 1,5,9,13-tetra-azatridecane bind with a lower affinity. The naturally occurring polyamines thus have a higher affinity for DNA than the related polyamines which do not occur naturally. 6. Binding of spermine or spermidine to DNA alters the spectrophotometric absorbance of DNA at 260 nm.     

Effect of magnesium on blood pressure.

Twenty patients receiving long term diuretic treatment for arterial hypertension (18 patients) or congestive heart failure (two patients) received magnesium supplementation as aspartate hydrochloride 15 mmol/day for six months. Both systolic and diastolic pressures decreased significantly, by a mean of 12/8 mm Hg. No significant changes were recorded in plasma or urinary electrolytes except for magnesium, 24 hour urinary volumes, or body weight after treatment. The effect of magnesium on blood pressure may be direct or through influences on the internal balance of potassium, sodium, and calcium.     

Antiviral activity of magnesium and magnesium/poly r(A-U) combinations against two RNA viruses.

Magnesium (Mg2+) potentiated the anti-vesicular stomatitis virus (VSV) activity of poly r(A-U) or poly r(G-C) and the anti-HIV-1 activity of poly r(A-U). Mg2+ did not affect the anti-VSV activity of poly (rI).poly (rC), poly (dA-dT).poly (dA-dT) or poly (dG-dC).poly (dG-dC). Modulation of one or more nuclear (nucleolar) processes of the host cell may be responsible for the synergistic antiviral activity.     

Fasting plasma magnesium concentrations and glucose disposal in diabetes.

Fasting plasma concentrations of magnesium were measured by neutron activation analysis in 30 non-diabetics and 87 diabetics (55 non-insulin-treated, 32 insulin treated). Plasma concentrations of magnesium were lowest in the insulin treated group (mean 0.84 (SEM 0.01) mmol/1; 2.0 (0.02) mg/100 ml), intermediate in the non-diabetics (mean 0.89 (SEM 0.01) mmol/1; 2.2 (0.02) mg/100 ml), and highest in the non-insulin-treated diabetics (mean 0.95 (SEM 0.02) mmol/1; 2.3 (0.05) mg/100 ml). In all diabetics plasma magnesium concentrations were inversely related to plasma glucose values (rs = -0.33; p less than 0.01) and in non-insulin-treated patients to plasma insulin concentrations (rs = -0.28; p less than 0.05), the former confirming previous observations. In 67 of the diabetics the KG constant for disposal rate of glucose during a standard intravenous glucose tolerance test was directly related to fasting plasma magnesium concentrations, and this relation persisted after controlling for age, sex, body mass index, type of treatment, and glucose and insulin values. This direct relation of plasma magnesium concentration with glucose disposal was unexplained by its influence on insulin secretion but was related to insulin sensitivity; hence magnesium may be an important determinant of insulin sensitivity in maturity onset diabetes.     

Changes in cellular composition during magnesium deficiency.

1. Concentrations and compositions of liver, serum and milk lipids of cows were measured during 6 days' starvation and serum lipids during 60 days' re-feeding. 2. The concentration of free fatty acid in serum increased fivefold during starvation. 3. The content of total lipid in liver (g/100g of liver dry matter) doubled owing to a 20-fold increase in triglyceride, an eightfold increase in cholesterol ester, a three fold increase in free fatty acid and a 20% increase in cholesterol. There were no changes in the content or composition of liver phospholipids. 4. Starvation lowered the concentrations of total lipid, phospholipid and cholesterol ester of dextran sulphate-precipitable serum lipoproteins. Total lipid and cholesterol ester concentrations in lipoproteins of d greater than 1.055 and in lipoproteins not precipitable by dextran sulphate decreased from day 4 of the starvation period and during the first 20 days' re-feeding. 5. During starvation there were decreases in percentages of stearic acid and increases in oleic acid in serum free fatty acids and triglycerides and in liver neutral lipid. 6. Throughout starvation total milk lipid yield decreased, yields and percentages of C4-14 fatty acids decreased and percentages of C18 fatty acids increased. 7. It is suggested that accumulation of triglyceride in liver may be caused by increased uptake of plasma free fatty acids without corresponding increase in lipoprotein secretion.     

Characterisation of magnesium nutrition and interaction of magnesium and potassium in rice

Magnesium (Mg) is known as one of the essential nutrients for higher plants; yet, the preliminary physiological responses of field crops to its deficiency or excess, particularly to its interaction with potassium (K), remain largely unknown. In this study, we observed that Mg deficiency in rice (Oryza sativa) [less than 1.1 mg g^?1 dry weight (DW) in the shoot] resulted in significant reduction in shoot biomass, decrease in total chlorophyll concentration and net photosynthetic rate and reduction in activities of both nitrate reductase [NR; enzyme classification (EC) 1.6.6.1] and glutamine synthetase (EC 6.3.1.2) in the leaves. However, the Mg‐deficient plant contained higher starch in the leaves, and partitioned larger biomass into roots. Excess of Mg (more than 3.0 mg g^?1 DW in the shoot), together with low K supply, suppressed NR activity and decreased concentration of soluble sugar in the leaves. There were great antagonistic and moderately synergistic effects between K and Mg, but the effects of K were much more significant than those of Mg on their uptake and translocation, NR activity and net photosynthetic rate in the leaves. The optimum weight ratio of K to Mg ranged between 22 and 25 in the leaves at tillering stage. Mg deficiency was not compensated for by moderate supply of K but was aggravated by excess supply of K, suggesting specific roles of Mg in both dry matter production and partition of carbon assimilates in rice.