Pyridoxine
PN. All 3-hydroxy-2-methylpyridines that are active as vitamins are subsumed as vitamin B6. A P is added to the phosphorylated compounds to simplify matters.
PN, PL and PM are absorbed in the small intestine by passive diffusion. The phosphates are hydrolysed by the membrane-bound alkaline phosphatase. They enter the liver or peripheral tissue via the bloodstream, where they are phosphorylated by PL kinase.
PNP is converted into the actual active form PLP by an oxidase. PLP and PMP can be reversibly converted into each other by many transaminases. Dephosphorylation is also possible.
PLP circulates in the blood bound to albumin, but in this form it has such a low turnover rate that it is equivalent to a depot form.
PLP is a coenzyme of numerous enzymes, especially in amino acid metabolism.
PMP also fulfils coenzyme functions, but only in transaminases. It is bound to a lysine residue of the enzyme.