Magnesium in biology
For example, adenosine triphosphate (ATP), the main source of energy in cells, must bind to a magnesium ion in order to be biologically active.
[7] Inadequate magnesium intake frequently causes muscle spasms, and has been associated with cardiovascular disease, diabetes, high blood pressure, anxiety disorders, migraines, osteoporosis, and cerebral infarction.
[8][9] Acute deficiency (see hypomagnesemia) is rare, and is more common as a drug side-effect (such as chronic alcohol or diuretic use) than from low food intake per se, but it can occur in people fed intravenously for extended periods of time.
[16] For other than pregnancy-related hypertension, a meta-analysis of 22 clinical trials with dose ranges of 120 to 973 mg/day and a mean dose of 410 mg, concluded that magnesium supplementation had a small but statistically significant effect, lowering systolic blood pressure by 3–4 mm Hg and diastolic blood pressure by 2–3 mm Hg.
[25] The U.S. Institute of Medicine (IOM) updated Estimated Average Requirements (EARs) and Recommended Dietary Allowances (RDAs) for magnesium in 1997.
For U.S. food and dietary supplement labeling purposes, the amount in a serving is expressed as a percent of daily value (%DV).
Not enough magnesium can lead to hypomagnesemia as described above, with irregular heartbeats, high blood pressure (a sign in humans but not some experimental animals such as rodents), insomnia, and muscle spasms (fasciculation).
[39][40] This suggests that different cell types may regulate influx and efflux of magnesium in different ways based on their unique metabolic needs.
In magnesium transport knockout strains of bacteria, healthy rates are maintained only with exposure to very high external concentrations of the ion.
[55] Mg2+ is the fourth-most-abundant metal ion in cells (per moles) and the most abundant free divalent cation — as a result, it is deeply and intrinsically woven into cellular metabolism.
In general, Mg2+ interacts with substrates through inner sphere coordination, stabilising anions or reactive intermediates, also including binding to ATP and activating the molecule to nucleophilic attack.
ATP (adenosine triphosphate), the main source of energy in cells, must be bound to a magnesium ion in order to be biologically active.
For instance, hexahydrated Mg2+ ions bind in the deep major groove and at the outer mouth of A-form nucleic acid duplexes.
[42] The Mg2+ ion tends to bind only weakly to proteins (Ka ≤ 105[56]) and this can be exploited by the cell to switch enzymatic activity on and off by changes in the local concentration of Mg2+.
[69] This limits the application of this dye to cell types where the resting level of Ca2+ is < 1 μM and does not vary with the experimental conditions under which Mg2+ is to be measured.
If the ion concentration is buffered by the cell by chelation or removal to subcellular compartments, the measured rate of uptake will give only minimum values of km and Vmax.
[citation needed] First, ion-specific microelectrodes can be used to measure the internal free ion concentration of cells and organelles.
[citation needed] Third, the technique of patch-clamp uses isolated sections of natural or artificial membrane in much the same manner as voltage-clamp but without the secondary effects of a cellular system.
[citation needed] Inductively coupled plasma (ICP) using either the mass spectrometry (MS) or atomic emission spectroscopy (AES) modifications also allows the determination of the total ion content of biological samples.
[73] The chemical and biochemical properties of Mg2+ present the cellular system with a significant challenge when transporting the ion across biological membranes.
This section will apply this knowledge to aspects of whole plant physiology, in an attempt to show how these processes interact with the larger and more complex environment of the multicellular organism.
Within individual plant cells, the Mg2+ requirements are largely the same as for all cellular life; Mg2+ is used to stabilise membranes, is vital to the utilisation of ATP, is extensively involved in the nucleic acid biochemistry, and is a cofactor for many enzymes (including the ribosome).
In the case of Mg2+, which is highly mobile in both the xylem and phloem,[86] the ions will be transported to the top of the plant and back down again in a continuous cycle of replenishment.
The diagram shows a schematic of a plant and the putative processes of Mg2+ transport at the root and leaf where Mg2+ is loaded and unloaded from the vascular tissues.
[78] These processes involve the release of Mg2+ from its bound and stored states and its transport back into the vascular tissue, where it can be distributed to the rest of the plant.
Likewise, the light-regulated Mg2+ concentration changes in chloroplasts are not fully understood, but do require the transport of H+ ions across the thylakoid membrane.
[94] Deshaies et al. had stated in their paper that older pea chloroplasts showed less significant changes in Mg2+ content than those used to form their conclusions.
The second class of enzymes includes those where the Mg2+ is complexed to nucleotide di- and tri-phosphates (ADP and ATP), and the chemical change involves phosphoryl transfer.
The first observable signs of Mg2+ stress in plants for both starvation and toxicity is a depression of the rate of photosynthesis, it is presumed because of the strong relationships between Mg2+ and chloroplasts/chlorophyll.
Stress responses in the plant develop as cellular processes halt due to a lack of Mg2+ (e.g. maintenance of ΔpH across the plasma and vacuole membranes).
