<Tr> <Td> </Td> <Td> </Td> </Tr> <P> Pyridoxal phosphate (PLP, pyridoxal 5' - phosphate, P5P), the active form of vitamin B, is a coenzyme in a variety of enzymatic reactions . The Enzyme commission has catalogued more than 140 PLP - dependent activities, corresponding to ~ 4% of all classified activities . The versatility of PLP arises from its ability to covalently bind the substrate, and then to act as an electrophilic catalyst, thereby stabilizing different types of carbanionic reaction intermediates . </P> <P> 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 (internal aldimine) 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 . </P> <P> In transamination, after deprotonation the quinoid intermediate accepts a proton at a different position to become a ketimine . The resulting ketimine is hydrolysed so that the amino group remains on the complex . In addition, PLP is used by aminotransferases (or transaminases) that act upon unusual sugars such as perosamine and desosamine . In these reactions, the PLP reacts with glutamate, which transfers its alpha - amino group to PLP to make pyridoxamine phosphate (PMP). PMP then transfers its nitrogen to the sugar, making an amino sugar . </P>

Where is vitamin b6 activated to form its active form pyridoxal phosphate (plp)