Pyridoxal-5'-phosphate PLP is the active form of vitamin B6 and plays a crucial role in amino acid metabolism and biosynthesis. It acts as a coenzyme for various enzymes involved in the transamination, decarboxylation, racemization, and other reactions of amino acids. These reactions are essential for the synthesis and breakdown of amino acids, as well as the production of various important biomolecules.1. Transamination: PLP is a coenzyme for transaminases aminotransferases , which catalyze the transfer of an amino group from an amino acid to an -keto acid. This reaction is essential for the synthesis of non-essential amino acids and the interconversion of amino acids. In this process, PLP forms a Schiff base with the amino group of the substrate amino acid, and the amino group is then transferred to the -keto acid, generating a new amino acid.2. Decarboxylation: PLP also acts as a coenzyme for decarboxylases, which catalyze the removal of a carboxyl group from amino acids. This reaction is important for the synthesis of various neurotransmitters and other biologically active molecules. For example, PLP-dependent decarboxylation of glutamate produces -aminobutyric acid GABA , a major inhibitory neurotransmitter in the central nervous system.3. Racemization: PLP is involved in the racemization of amino acids, which is the interconversion of L- and D-amino acids. This reaction is catalyzed by PLP-dependent racemases and is important for the synthesis of D-amino acids, which are found in certain proteins and peptides.4. Other reactions: PLP also participates in other reactions of amino acids, such as the synthesis of cysteine from serine by cystathionine -synthase, the synthesis of heme from glycine and succinyl-CoA by aminolevulinic acid synthase, and the breakdown of tryptophan by tryptophanase.In summary, pyridoxal-5'-phosphate PLP plays a vital role in amino acid metabolism and biosynthesis by acting as a coenzyme for various enzymes involved in transamination, decarboxylation, racemization, and other reactions. These processes are essential for the synthesis and breakdown of amino acids, as well as the production of important biomolecules such as neurotransmitters and heme.