What is Magnesium transporters
All forms of life require magnesium, and yet the molecular mechanisms of Mg2+ uptake from the environment and the distribution (transport) of this vital element within the organism are only slowly being elucidated. In bacteria Mg2+ is probably mainly supplied by the CorA protein[1] and, where the CorA protein is absent, by the MgtE protein[2][3]. In yeast the initial uptake is via the Alr1p and Alr2p proteins[4], but at this stage the only internal Mg2+ distributing protein identified is Mrs2p[5]. Within the protozoa only one Mg2+ transporter (XntAp) has been identified[6]. In metazoa, Mrs2p[7] and MgtE homologues[8] have been identified, along with two novel Mg2+ transport systems TRPM6/TRPM7[9][10] and PCLN-1[11]. Finally, in plants, a family of Mrs2p homologues has been identified[12][13] along with another novel protein, AtMHX[14].
The evolution of Mg2+ transport appears to have been rather complicated. Proteins apparently based on MgtE are present in bacteria and metazoa, but are missing from fungi and plants, whilst proteins apparently related to CorA are present in all of these groups. The two active-transport transporters present in bacteria, MgtA and MgtB, do not appear to have any homologues in the higher organisms. There are also Mg2+ transport systems that are found only in the higher organisms.
Clearly there are a large number of proteins yet to be identified that transport Mg2+. Even in the best studied eukaryote, yeast, Borrelly[15] have reported a Mg2+/H+ exchanger, without an associated protein, which is probably localised to the Golgi. At least one other major Mg2+ transporter in yeast still unaccounted for — that effecting Mg2+ transport into and out of the yeast vacuole. In higher, multicellular organisms it seems that many Mg2+ transporting proteins await discovery.
The CorA-domain-containing Mg2+ transporters (CorA, Alr-like and Mrs2-like) have a similar but not identical array of affinities for divalent cations. In fact, this observation can be extended to all of the Mg2+ transporters so far identified. This similarity suggests that the basic properties of Mg2+ strongly influence the possible mechanisms of recognition and transport. However, this observation also suggests that using other metal ions as tracers for Mg2+ uptake will not necessarily produce results comparable to the transporter’s ability to transport Mg2+. Ideally, Mg2+ should be measured directly[16].
In a world where 28Mg2+ is practically unobtainable, much of the old data will need to be reinterpreted in terms of new tools for measuring Mg2+ transport, if different transporters are to be compared directly. The pioneering work of Kolisek[17] and Froschauer[18] using mag-fura 2 has shown that free Mg2+ can be reliably measured in vivo in some systems. By returning to the analysis of CorA with this new tool, we have gained an important baseline for the analysis of new Mg2+ transport systems as they are discovered. However, it is important that the amount of transporter present in the membrane is accurately determined if comparisons of transport capability are to be made. This bacterial system might also be able to provide some utility for the analysis of eukaryotic Mg2+ transport proteins. However, the differences in biological systems between prokaryotes and eukaryotes will have to be considered as part of any experiment.
Comparing the functions of the characterised Mg2+ transport proteins is currently almost impossible. The proteins have been investigated in different biological systems using different methodologies and technologies. Finding a system where all the proteins can be compared directly would be a major advance. If the proteins could be shown to be functional in bacteria (S. typhimurium) then a combination of the techniques of mag-fura 2, quantification of protein in the envelope membrane, and structure of the proteins (X-ray crystal or cryo-TEM) might allow the determination of the basic mechanisms involved in the recognition and transport of the Mg2+ ion. However, perhaps the best advance would be the development of methods allowing the measurement of the protein’s function in the patch-clamp system using artificial membranes.
Tags: Integral membrane proteins, Ion channels, Membrane proteins, Proteins, Transmembrane proteins
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The Mg2+ cation is the second most abundant cation in seawater (occurring at about 12% of the mass of sodium there), which makes seawater and sea-salt an attractive commercial source of Mg. To extract the magnesium, calcium carbonate is added to sea water to form magnesium carbonate precipitate.
MgCl2 + CaCO3 ? MgCO3 + CaCl2
Magnesium carbonate is insoluble in water so it can be filtered out, and reacted with hydrochloric acid to obtain concentrated magnesium chloride.
MgCO3 + 2HCl ? MgCl2 + CO2 + H2O
From magnesium chloride, electrolysis produces magnesium.
See also: Category:Magnesium minerals
There are two classes of glutamate transporters, those that are dependent on an electrochemical gradient of sodium ions (the EAATs) and those that are not (VGluTs).[5] Some sodium independent transporters such as the cystein-glutamate antiporter are localised to plasma membrane of cells whilst others the are called vesicular transporters. Na+-dependent transporters are actually also dependent on K+ concentrations, and so are also known as 'sodium and potassium coupled glutamate transporters' or, in humans, 'excitatory amino acid transporters' (EAATs).[6] Some Na+-dependent transporters have also been called 'high-affinity transporters', though their glutamate affinity actually varies widely.[6]
mitochondria also possess mechanisms for taking up
The magnesium ion is necessary for all life (see magnesium in biology), so magnesium salts are an additive for foods, fertilizers (Mg is a component of chlorophyll), and culture media.
Magnesium hydroxide is used in milk of magnesia, its chloride, oxide, gluconate, malate, orotate and citrate used as oral magnesium supplements, and its sulfate (Epsom salts) for various purposes in medicine, and elsewhere (see the article for more). Oral magnesium supplements have been claimed to be therapeutic for some individuals who suffer from Restless Leg Syndrome (RLS).[citation needed]
Magnesium borate, magnesium salicylate and magnesium sulfate are used as antiseptics.
Magnesium bromide is used
In enzymology, a magnesium protoporphyrin IX methyltransferase (EC 2.1.1.11) is an enzyme that catalyzes the chemical reaction
S-adenosyl-L-methionine + magnesium protoporphyrin IX S-adenosyl-L-homocysteine + magnesium protoporphyrin IX 13-methyl ester
Thus, the two substrates of this enzyme are S-adenosyl methionine and magnesium protoporphyrin IX, whereas its two products are S-adenosylhomocysteine and magnesium protoporphyrin IX 13-methyl ester.
This enzyme belongs to the family of transferases, specifically those transferring one-carbon group methyltransferases. The systematic name of this enzyme class is S-adenosyl-L-methionine:magnesium-protoporphyrin-IX O-methyltransferase. This enzyme participates in porphyrin and chlorophyll metabolism.
In enzymology, a magnesium chelatase (EC 6.6.1.1) is an enzyme that catalyzes the chemical reaction
ATP + protoporphyrin IX + Mg2+ + H2O ADP + phosphate + Mg-protoporphyrin IX + 2 H+
The 4 substrates of this enzyme are ATP, protoporphyrin IX, Mg2+, and H2O, whereas its 4 products are ADP, phosphate, Mg-protoporphyrin IX, and H+.
This enzyme belongs to the family of ligases, specifically those forming nitrogen-D-metal bonds in coordination complexes. The systematic name of this enzyme class is Mg-protoporphyrin IX magnesium-lyase. Other names in common use include protoporphyrin IX magnesium-chelatase, protoporphyrin IX Mg-chelatase, magnesium-protoporphyrin IX chelatase, magnesium-protoporphyrin chelatase, magnesium-chelatase, Mg-chelatase,
Magnesium metal and alloys are highly flammable in their pure form when molten, as a powder, or in ribbon form. Burning or molten magnesium metal reacts violently with water. Magnesium powder is an explosive hazard. One should wear safety glasses while working with magnesium, and if burning it, these should include a heavy U.V. filter, similar to welding eye protection. The bright white light (including ultraviolet) produced by burning magnesium can permanently damage the retinas of the eyes, similar to welding arc burns.[16]
Water should not be used to extinguish magnesium fires, because it can produce hydrogen which will feed the
Magnesium (pronounced /mæg?ni?zi?m/) is a chemical element with the symbol Mg, atomic number 12, atomic weight 24.3050 and common oxidation number +2.
Magnesium, an alkaline earth metal, is the ninth most abundant element in the universe by mass.[1] It constitutes about 2% of the Earth's crust by mass, which makes it the eighth most abundant element in the crust.[2] It is the third most abundant element dissolved in seawater.[citation needed]
Magnesium is the 11th most abundant element by mass in the human body; its ions are essential to all living cells, but nearly 50% is found within the bones.[citation needed] The free
Specific types of neurotransmitter transporters include the following:
GABA transporters, including:
GABA transporter type 1 (GAT-1)
GABA transporter type 2 (GAT-2)
GABA transporter type 3 (GAT-3)
Betaine transporter (BGT-1)
Vesicular GABA transporter (VGAT)
Glutamate transporters
Glutamine transporters[5]
Glycine transporters, including:
Glycine transporter type 1 (GlyT-1)
Glycine transporter type 2 (GlyT-2)
Monoamine transporters including:
The dopamine transporter, DAT.
The norepinephrine transporter, NET.
The serotonin transporter, SERT.
Vesicular acetylcholine transporters[6]
Vesicular monoamine transporters
Excitatory Amino Acid Transporters (EAAT), formerly known as Glutamate transporters, belong to the family of neurotransmitter transporters. They serve to terminate the excitatory neurotransmitter signal by removal (uptake) of glutamate from the neuronal synapse into Glia cells.
In details, the EAATs are membrane-bound pumps that resemble ion channels.[1] These transporters play the important role of regulating concentrations of glutamate in the extracellular space, keeping it at low levels.[2] After glutamate is released as the result of an action potential, glutamate transporters quickly remove it from the extracellular space to keep its levels low, thereby terminating the synaptic transmission.[1][3]
Without the activity of
ATP-binding domain of ABC transporters is a water-soluble domain of transmembrane ABC transporters.
ABC transporters belong to the ATP-Binding Cassette superfamily, which uses the hydrolysis of ATP to translocate a variety of compounds across biological membranes. ABC transporters are minimally constituted of two conserved regions: a highly conserved ATP binding cassette (ABC) and a less conserved transmembrane domain (TMD). These regions can be found on the same protein or on two different ones. Most ABC transporters function as a dimer and therefore are constituted of four domains, two ABC modules and two TMDs.
In 1968 Lusk[19] described the limitation of bacterial (Escherichia coli) growth on Mg2+-poor media, suggesting that bacteria required Mg2+ and were likely to actively take up this ion from the environment. The following year the same group[20] and another group, Silver[21], independently described the uptake and efflux of Mg2+ in metabolically active E. coli cells using 28Mg2+. By the end of 1971 two papers had been published describing the interference of Co2+, Ni2+ and Mn2+ on the transport of Mg2+ in E. coli[22] and in Aerobacter aerogenes and Bacillus megaterium[23]. In a last major development prior to the cloning of
Currently, five types of SMase have been identified. These are classified according to their cation dependence and pH optima of action and are:
Lysosomal Acid SMase
Secreted zinc-dependent Acid SMase
Magnesium-dependent Neutral SMase
Magnesium-independent Neutral SMase
Alkaline SMase
Of these, the lysosomal acidic SMase and the magnesium-dependent neutral SMase are considered major candidates for the production of ceramide in the cellular response to stress.
Neurotransmitter transporters are proteins that span cellular membranes and that serve to carry neurotransmitters across these membranes and to transport them to specific locations. There are more than twenty types of neurotransmitter transporters.[1] The transporters exist in the membranes of neurons and glia.
Vesicular transporters move neurotransmitters into synaptic vesicles, regulating the concentrations of substances within them.[2] Vesicular transporters rely on a proton gradient created by the hydrolysis of adenosine triphosphate (ATP) in order to carry out their work: vesicle ATPase hydrolyzes ATP, causing protons to be pumped into the vesicle and creating a proton gradient. Then the efflux of protons
The investigation of Mg2+ in animals, including humans, has lagged behind that in bacteria and yeast. This is largely because of the complexity of the systems involved, but it is also due to the impression within the field that Mg2+ was maintained at high levels within all cells and was unchanged by external influences. Only in the last 25 years has a series of reports begun to challenge this view, with new methodologies finding that free Mg2+ content is maintained at levels where changes might influence cellular metabolism
The name originates from the Greek word for a district in Thessaly called Magnesia. It is related to magnetite and manganese, which also originated from this area, and required differentiation as separate substances. See manganese for this history.
Magnesium is the seventh most abundant element in the earth's crust by mass and eighth by molarity.[2] It is found in large deposits of magnesite, dolomite, and other minerals, and in mineral waters, where magnesium ion is soluble. In 1618 a farmer at Epsom in England attempted to give his cows water from a well. They refused to drink because of the water's
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