Pyridoxal Phosphate (PLP)

Pyridoxal-phosphate isthe active form of vitamin B6, which comprises three natural organic compounds, pyridoxal, pyridoxamine and pyridoxine. This co-factor acts as an electron sink to stabilize carbanionic intermediates in both substitution and elimination reactions involving aminated compounds. PLP acts as a coenzyme in all transamination reactions, and in certain decarboxylation, deamination, and racemization reactions of amino acids. The aldehyde group of PLP forms a Schiff-base linkage with the ε-amino group of a specific lysine 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 in a process known as transaldimination. The resulting external aldimine can lose a proton, carbon dioxide, or an amino acid sidechain to become a quinoid intermediate, which in turn can act as a nucleophile in several reaction pathways.