Editing Vitamin B6 (section)

==Definition==
[[File:Pyridoxin.svg|thumb|120px|class=skin-invert-image|Pyridoxine (PN)]]
[[File:Pyridoxamin.svg|thumb|120px|class=skin-invert-image|Pyridoxamine (PM)]]
[[File:Pyridoxal2.svg|thumb|120px|class=skin-invert-image|Pyridoxal (PL)]]
Vitamin B<sub>6</sub> is a water-soluble [[vitamin]], one of the B vitamins. The vitamin actually comprises a group of six chemically related compounds, i.e., [[vitamer]]s, that all contain a [[pyridine]] ring as their core. These are [[pyridoxine]], [[pyridoxal]], [[pyridoxamine]], and their respective [[phosphorylation|phosphorylated]] derivatives [[pyridoxine 5'-phosphate]], [[Pyridoxal phosphate|pyridoxal 5'-phosphate]] and [[pyridoxamine 5'-phosphate]]. Pyridoxal 5'-phosphate has the highest [[biological activity]], but the others are convertible to that form.<ref name="Bachman2018">{{cite journal |vauthors=Bachmann T, Rychlik M |title=Synthesis of [13C₃]-B6 Vitamers Labelled at Three Consecutive Positions Starting from [13C₃]-Propionic Acid |journal=Molecules |volume=23 |issue=9 |pages= |date=August 2018 |pmid=30142892 |pmc=6225105 |doi=10.3390/molecules23092117 |url=|doi-access=free }}</ref> Vitamin B<sub>6</sub> serves as a [[Cofactor (biochemistry)|co-factor]] in more than 140 cellular reactions, mostly related to [[amino acid]] biosynthesis and catabolism, but is also involved in [[fatty acid]] biosynthesis and other physiological functions.<ref name=ODS/><ref name="lpi"/><ref name=PKIN2020B6 />

===Forms===
Because of its chemical stability, pyridoxine hydrochloride is the form most commonly given as vitamin B<sub>6</sub> dietary supplement. Absorbed pyridoxine (PN) is converted to pyridoxamine 5'-phosphate (PMP) by the enzyme [[pyridoxal kinase]], with PMP further converted to pyridoxal 5'-phosphate (PLP), the metabolically active form, by the enzymes [[pyridoxamine-phosphate transaminase]] or [[pyridoxine 5'-phosphate oxidase]], the latter of which also catalyzes the conversion of pyridoxine 5′-phosphate (PNP) to PLP.<ref name=PKIN2020B6 /><ref name="Bachman2018"/> Pyridoxine 5'-phosphate oxidase is dependent on [[flavin mononucleotide]] (FMN) as a cofactor produced from [[riboflavin]] (vitamin B<sub>2</sub>). For degradation, in a non-reversible reaction, PLP is [[Catabolism|catabolized]] to 4-pyridoxic acid, which is excreted in urine.<ref name=PKIN2020B6 />