Glutamate (neurotransmitter)
Glutamate is a major constituent of a wide variety of proteins; consequently it is one of the most abundant amino acids in the human body. Under ordinary conditions enough is obtained from the diet that there is no need for any to be synthesized. Nevertheless, glutamate is formally classified as a non-essential amino acid, because it can be synthesized from alpha-Ketoglutaric acid, which is produced as part of the citric acid cycle by a series of reactions whose starting point is citrate. Glutamate cannot cross the blood-brain barrier unassisted, but it is actively transported into the nervous system by a high affinity transport system, which maintains its concentration in brain fluids at a fairly constant level.
Magnesium in biology
Mg 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. Indeed, Mg-dependent enzymes appear in virtually every metabolic pathway: Specific binding of Mg to biological membranes is frequently observed, Mg is also used as a signalling molecule, and much of nucleic acid biochemistry requires Mg, including all reactions that require release of energy from ATP. In nucleotides, the triple-phosphate moiety of the compound is invariably stabilized by association with Mg in all enzymatic processes.