[5] 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.

The resulting external aldimine can lose a proton, carbon dioxide, or an amino acid sidechain to become a quinonoid intermediate, which in turn can act as a nucleophile in several reaction pathways.

[11] Human Serine hydroxymethyltransferase 2 regulates one-carbon transfer reactions required for amino acid and nucleotide metabolism, and exists in dimeric and tetrameric forms.

The dimeric SHMT2 variant is a potent inhibitor of the BRISC deubiquitylase enzyme complex, which regulates immune-based cell signaling.

This prevents interaction with the BRISC deubiqutylase complex, potentially linking vitamin B6 levels and metabolism to inflammation.

Although the scope of PLP-catalyzed reactions appears to be immense, the unifying principle is the formation of an internal lysine-derived aldimine.

Once the amino substrate interacts with the active site, a new Schiff base is generated, commonly referred to as the external aldimine.

[14] Animals are auxotroph for this enzyme co-factor and require it or an intermediate to be supplemented, hence its classification as a vitamin B6, unlike MoCo or CoQ10 for example.

[18] The final enzyme is PNP oxidase (pdxH), which catalyzes the oxidation of the 4' hydroxyl group to an aldehyde using dioxigen, resulting in hydrogen peroxide.

A "serendipitous pathway" was found in an overexpression library that could suppress the auxotrophy caused by the deletion of pdxB (encoding erythronate 4 phosphate dehydrogenase) in E. coli.

3PHP was dephosphorylated, resulting in an unstable intermediate that decarboxylates spontaneously (hence the presence of the phosphate in the serine biosynthetic pathway) to glycaldehyde.

[21] The widespread utilization of PLP in central metabolism, especially in amino acid biosynthesis, and its activity in the absence of enzymes, suggests PLP may be a "prebiotic" compound—that is, one that predates the origin of organic life (not to be confused with prebiotic compounds, substances which serve as a food source for beneficial bacteria).

[22] Under certain conditions, PLP is formed from cyanoacetylene, diacetylene, carbon monoxide, hydrogen, water, and a phosphoric acid.

Overall, in the PLP-dependent enzymes, the PLP in every case is covalently attached via an imine bond to the amino group in the active site.