Introduction

Magnesium is an essential element in biological systems. Magnesium occurs typically as the Mg²⁺ ion. It is an essential mineral nutrient for life (Leroy, 1926; Lusk et al., 1968; Marschner, 1995) and is present in every cell type in every organism. In animals it has been shown that individual cell types maintain differing levels of magnesium (Valberg et al., 1965; Seiler et al., 1966; Walser, 1967; Iyengar et al., 1978) and it seems likely that the same is true for plants (Stelzer et al., 1990; Shaul et al., 1999). This suggests that the balance of uptake and efflux of magnesium may be regulated in different ways in different cell types. A delicate balance of internal free magnesium must also be maintained for the correct function of the cell by the combined processes of buffering (binding of ions to proteins and other molecules) and muffling (the transport of ions to storage or extracellular spaces; (Thomas et al., 1991). Additionally, in plants, and more recently in animals, it has been recognised that magnesium is an important regulatory signal, both activating and mediating many biochemical reactions. The best example of this is perhaps the regulation of key enzymes involved in the fixation of carbon in chloroplasts (reviewed in Berkowitz and Wu, 1993 and Shaul, 2002). Nutrients and the body A nutrient is any element or compound necessary for or contributing to an organisms metabolism, growth, or other functioning. ... A cell is a single unit or compartment, enclosed by a border or wall. ... Phyla dude i hate you mom she is really really fat!!haha!***Porifera (sponges) Ctenophora (comb jellies) Cnidaria (coral, jellyfish, anenomes) Placozoa (trichoplax) Subregnum Bilateria (bilateral symmetry) Acoelomorpha (basal) Orthonectida (flatworms, echinoderms, etc. ... Divisions Green algae land plants (embryophytes) non-vascular embryophytes Hepatophyta - liverworts Anthocerophyta - hornworts Bryophyta - mosses vascular plants (tracheophytes) seedless vascular plants Lycopodiophyta - clubmosses Equisetophyta - horsetails Pteridophyta - true ferns Psilotophyta - whisk ferns Ophioglossophyta - adderstongue ferns seed plants (spermatophytes) †Pteridospermatophyta - seed ferns Pinophyta - conifers Cycadophyta - cycads Ginkgophyta - ginkgo Gnetophyta - gnetae Magnoliophyta - flowering... Ribbon diagram of the catalytically perfect enzyme TIM. Factor D enzyme crystal prevents the immune system from inappropriately running out of control. ... General Name, Symbol, Number carbon, C, 6 Chemical series nonmetals Group, Period, Block 14, 2, p Appearance black (graphite) colorless (diamond) Atomic mass 12. ... The inside of a chloroplast The inside of a chloroplast Chloroplasts are organelles found in plant cells and eukaryotic algae which conduct photosynthesis. ...

As magnesium is important to each individual cell, deficiency will cause disease phenotypes in the affected organism. In single-celled organisms the phenotype is very easy to see; bacteria and yeast both show greatly reduced growth rates when magnesium is limiting. Additionally, when the magnesium uptake systems are deleted genetically from these organisms they must be supplemented with very high external concentrations of magnesium to achieve normal growth rates (Hmiel et al., 1989; MacDiarmid and Gardner, 1998). In yeast, magnesium deficiency in a subcellular compartment, the mitochondria, also leads to a disease state (Wiesenberger et al., 1992). In animals, magnesium deficiency (hypomagnesemia or ‘grass tetany’) is seen in ruminant animals when the environmental availability of magnesium is low, and is identified by a loss of balance due to muscle weakness (Grunes et al., 1970). A number of genetically attributable hypomagnesmia disorders have also been identified in humans (Paunier et al., 1968; Weber et al., 2000; Weber et al., 2001; Chubanov et al., 2004). Plant stress responses can be observed in plants that are under supplied with magnesium. The first observable signs of magnesium stress in plants for both starvation and toxicity is a depression of the rate of photosynthesis, presumably because of the strong relationships between magnesium and chloroplasts/chlorophyll. The later effects of magnesium deficiency on plants are a significant reduction in growth and reproductive viability (Marschner, 1995). A disease is any abnormal condition of the body or mind that causes discomfort, dysfunction, or distress to the person affected or those in contact with the person. ... The phenotype of an individual organism is either its total physical appearance and constitution, or a specific manifestation of a trait, such as size or eye color, that varies between individuals. ... Kingdoms/Phyla/Divisions Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular: bacterium) are a major group of living organisms. ... Yeasts constitute a group of single-celled (unicellular) fungi, a few species of which are commonly used to leaven bread , ferment alcoholic beverages, and even drive experimental fuel cells. ... In cell biology, a mitochondrion is an organelle found in the cells of most eukaryotes. ... Leaf. ... Chlorophyll is a green photosynthetic pigment found in plants, algae, and cyanobacteria. ...

Equally clear is that over-accumulation of magnesium will lead to toxic effects on the cell. These effects have been much more difficult to show experimentally in single cells. However, in humans magnesium overload is well documented (usually caused by loss of function in the kidneys; (Harrison’s Principles of Internal Medicine, Online Edition) and magnesium can also be toxic to plants, although accompanying drought stress is generally required (Kaiser, 1987; Rao et al., 1987). Human kidneys viewed from behind with spine removed The kidneys are bean-shaped excretory organs in vertebrates. ... A drought adam+ahmed=morron is an extended period where water availability falls below the statistical requirements for a region. ...

So a balance of magnesium is vital to the well being of an organism. But what is it about magnesium that has led to its status as an indispensable component of cells? Magnesium is a relatively abundant ion in the lithosphere and is highly bioavailable in the hydrosphere. This ready availability, in combination with a useful and very unusual chemistry, may have led to its evolution as an ion for signalling, enzyme activation and catalysis. However, the unusual nature of ionic magnesium has also led to a major challenge in the use of the ion in biological systems. Biological membranes are impermeable to Mg²⁺ (and other ions) so transport proteins must facilitate the flow of Mg²⁺, both into and out of cells and intracellular compartments. The lithosphere (from the Greek for rocky sphere) is the solid outermost shell of a rocky planet. ... Hydrosphere (Greek hydro- means water) in physical geography, describes the collective mass of water found on, under, and over the surface of a planet. ... Generic graph showing the effect of a catalyst in an hypotetical exothermic chemical reaction. ...

Biological chemistry

Mg²⁺ is the fourth most abundant metal ion in cells (in moles) and the most abundant free divalent cation — as a result it is deeply and intrinsically woven into cellular metabolism. Indeed, Mg²⁺-dependent enzymes appear in virtually every metabolic pathway, much of nucleic acid biochemistry requires Mg²⁺, specific binding of Mg²⁺ to biological membranes is frequently observed, Mg²⁺ is required for the release of energy from ATP and Mg²⁺ is also used as a signalling molecule (reviewed in Cowan 1995; Romani and Maguire, 2002; Shaul, 2002). In photosynthetic organisms Mg²⁺ has the additional vital role of being the coordinating ion in the chlorophyll molecule. This role was discovered by R. M. Willstätter who received the Nobel Prize in Chemistry 1915 for the purification and structure of chlorophyll. Hot metal work from a blacksmith In chemistry, a metal (Greek: Metallon) is an element that readily forms ions (cations) and has metallic bonds, and metals are sometimes described as a lattice of positive ions (cations) in a cloud of electrons. ... An ion is an atom or group of atoms with a net electric charge. ...

The chemistry of the Mg²⁺ ion, as applied to enzymes, uses the full range of this ion’s unusual reaction chemistry to fulfil a range of functions (reviewed in Black and Cowan, 1995a; Black and Cowan, 1995b; Cowan, 1995; Cowan, 2002). Mg²⁺ interacts with substrates, enzymes and occasionally both (Mg²⁺ may form part of the active site). Mg²⁺ generally interacts with substrates through inner sphere coordination, stabilising anions or reactive intermediates, also including binding to ATP and activating the molecule to nucleophilic attack. When interacting with enzymes and other proteins Mg²⁺ may bind using inner or outer sphere coordination, to either alter the conformation of the enzyme or take part in the chemistry of the catalytic reaction. In either case, because Mg²⁺ is only rarely fully dehydrated during ligand binding, it may be a water molecule associated with the Mg²⁺ that is important rather than the ion itself. The Lewis acidity of Mg²⁺ (pKa 11.4) is used to allow both hydrolysis and condensation reactions (most commonly phosphate ester hydrolysis and phosphoryl transfer) that would otherwise require pH values greatly removed from physiological values.

Nucleic acids have an important range of interactions with Mg²⁺. The binding of Mg²⁺ to DNA and RNA stabilises structure; this can be observed in the increased melting temperature (Tm) of double-stranded DNA in the presence of Mg²⁺ (Cowan, 1995). Additionally, ribosomes contain large amounts of Mg²⁺ and the stabilisation provided is essential to the complexation of this ribo-protein (Sperrazza and Spremulli, 1983). A large number of enzymes involved in the biochemistry of nucleic acids bind Mg²⁺ for activity, using the ion for both activation and catalysis. Finally, the autocatalysis of many ribozymes (enzymes containing only RNA) is Mg²⁺ dependent (e.g. the yeast mitochondrial group II self splicing introns; see Smith, 1995). A nucleic acid is a complex, high-molecular-weight biochemical macromolecule composed of nucleotide chains that convey genetic information. ... Space-filling model of a section of DNA molecule Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions specifying the biological development of all cellular forms of life (and most viruses). ... Ribonucleic acid (RNA) is a nucleic acid polymer consisting of covalently bound nucleotides. ... Figure 1: Ribosome structure indicating small subunit (A) and large subunit (B). ... A ribozyme, or RNA enzyme, is an RNA molecule that can catalyze a chemical reaction. ...

Biological cell membranes and cell walls are polyanionic surfaces. This has important implications for the transport of ions, particularly because it has been shown that different membranes preferentially bind different ions (Cowan, 1995). Both Mg²⁺ and Ca²⁺ regularly stabilise membranes by the cross-linking of carboxylated and phosphorylated head groups of lipids. However, the envelope membrane of E. coli has also been shown to bind Na⁺, K⁺, Mn²⁺ and Fe³⁺. The transport of ions is dependent on both the concentration gradient of the ion and the electric potential (ΔΨ) across the membrane, which will be affected by the charge on the membrane surface. For example, the specific binding of Mg²⁺ to the chloroplast envelope has been implicated in a loss of photosynthetic efficiency by the blockage of K⁺ uptake and the subsequent acidification of the chloroplast stroma (Berkowitz and Wu, 1993). Drawing of a cell membrane A component of every biological cell, the selectively permeable cell membrane (or plasma membrane or plasmalemma) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ... A cell wall is a more or less solid layer surrounding a cell. ... The inside of a chloroplast The inside of a chloroplast Chloroplasts are organelles found in plant cells and eukaryotic algae which conduct photosynthesis. ...

The Mg²⁺ ion tends to bind only weakly to proteins (Ka ≤ 10⁵ M^-1; Cowan, 1995), and this can be exploited by the cell to switch enzymatic activity on and off by changes in the local concentration of Mg²⁺. Although the concentration of free cytoplasmic Mg²⁺ is on the order of 1 mM, the total Mg2+ content of animal cells is 30 mM (Ebel and Gunther, 1980) and in plants the content of leaf endodermal cells has been measured at values as high as 100 mM (Stelzer et al., 1990), much of which is buffered in storage compartments. The cytoplasmic concentration of free Mg²⁺ is buffered by binding to chelators (e.g. ATP), but also more importantly by storage of Mg²⁺ in intracellular compartments. The transport of Mg²⁺ between intracellular compartments may be a major part of regulating enzyme activity. The interaction of Mg2+ with proteins must also be considered for the transport of the ion across biological membranes. A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Neuraminidase ribbon diagram An enzyme (in Greek en = in and zyme = blend) is a protein, or protein complex, that catalyzes a chemical reaction and also controls the 3D orientation of the catalyzed substrates. ...

In biological systems only manganese (Mn²⁺) is readily capable of replacing Mg²⁺, and only in a limited set of circumstances. Mn²⁺ is very similar to Mg²⁺ in terms of its chemical properties, including inner and outer shell complexation. Mn²⁺ effectively binds ATP and allows hydrolysis of the energy molecule by most ATPases. Mn²⁺ can also replace Mg²⁺ as the activating ion for a number of Mg²⁺-dependent enzymes, although some enzyme activity is usually lost (Cowan, 1995). General Name, Symbol, Number manganese, Mn, 25 Chemical series transition metals Group, Period, Block 7, 4, d Appearance silvery metallic Atomic mass 54. ...