Pyridoxal-phosphate
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Pyridoxal-phosphate (PLP, pyridoxal-5'-phosphate) is a cofactor of many enzymatic reactions. It is the active form of vitamin B6 which is comprised of three natural organic compounds, pyridoxal, pyridoxamine and pyridoxine.
PLP acts as a coenzyme in all transaminations, and in some decarboxylation and dehydration reactions of amino acids. The aldehyde group of PLP forms a Schiff-base linkage with the ε-amino group of a specific alysine group of the aminotransferase enzyme. The α-amino group of the amino acid substrate displaces the ε-amino group of the active-site lysine residue. The resulting aldimine becomes deprotonated to become a quinoid intermediate, which in turn accepts a proton at a different position to become a ketimine. The resulting ketimine is hydrolysed that the amino group remains on the complex. It is also active in the condensation reaction in heme synthesis. It is produced from pyridoxal by the enzyme pyridoxal kinase, and it requires one ATP. It is metabolized in the liver.