PyridonePyridone may refer to several organic compounds with the formula :2-Pyridone3-hydroxypyridine4-PyridoneThese can adopt three tautomers, a oxo form, a zwitterion form, and a enol form. Whereas 2-pyridone and 4-pyridone predominantly adopt the oxo form, the 3-pyridone cannot, and instead adopts an equilibrium of the zwitterion form, pyridin-1-ium-3-olate, and the enol form, 3-hydroxypyridine. The 3-pyridone is not mesoionic. This property of 3-hydroxypyridine is leveraged in biology in pyridoxal phosphate: this common cofactor that catalyses a variety of reactions thanks to a stable cationic form.