Editing Biotin (section)

==Cofactor biochemistry==
The enzyme [[holocarboxylase synthetase]] covalently attaches biotin to five human [[carboxylase]] [[enzyme]]s:<ref name=PKIN2020Biotin />
* [[Acetyl-CoA carboxylase|Acetyl-CoA carboxylase alpha]] (ACC1)
* [[Acetyl-CoA carboxylase|Acetyl-CoA carboxylase beta]] (ACC2)
* [[Pyruvate carboxylase]] (PC)
* [[Methylcrotonyl-CoA carboxylase]] (MCC)
* [[Propionyl-CoA carboxylase]] (PCC)

For the first two, biotin serves as a [[Cofactor (biochemistry)|cofactor]] responsible for the transfer of [[bicarbonate]] to [[acetyl-CoA]], converting it to [[malonyl-CoA]] for [[fatty acid synthesis]]. PC participates in [[gluconeogenesis]]. MCC catalyzes a step in [[leucine]] metabolism. PCC catalyzes a step in the metabolism of [[propionyl-CoA]].<ref name=ods/><ref name=lpi/><ref name=PKIN2020Biotin /> Metabolic degradation of the [[biotinylation|biotinylated]] carboxylases leads to the formation of [[biocytin]]. This compound is further degraded by biotinidase to release biotin, which is then reutilized by holocarboxylase synthetase.<ref name=PKIN2020Biotin />

Biotinylation of [[histone]] proteins in nuclear chromatin is a [[posttranslational modification]] that plays a role in chromatin stability and gene expression.<ref name=PKIN2020Biotin /><ref name=Xu2014/>