Homocitric acid is an organic compound with the formula HOC(CO₂H)(CH₂CO₂H)(C₂H₄CO₂H). This tricarboxylic acid occurs naturally as a component of the iron-molybdenum cofactor of certain nitrogenase proteins.^[1] Biochemists often refer to this cofactor as homocitrate, which is the conjugate bases that predominate in neutral aqueous solutions of this species.

Homocitric acid

Names
Preferred IUPAC name 2-Hydroxybutane-1,2,4-tricarboxylic acid
Other names Homocitric acid Homocitrate
Identifiers
CAS Number	3562-74-1 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:17852 N
ChemSpider	26392 N
KEGG	C01251 N
PubChem CID	28371
UNII	5883XD8HH4 Y
InChI InChI=1S/C7H10O7/c8-4(9)1-2-7(14,6(12)13)3-5(10)11/h14H,1-3H2,(H,8,9)(H,10,11)(H,12,13) N Key: XKJVEVRQMLKSMO-UHFFFAOYSA-N N InChI=1/C7H10O7/c8-4(9)1-2-7(14,6(12)13)3-5(10)11/h14H,1-3H2,(H,8,9)(H,10,11)(H,12,13) Key: XKJVEVRQMLKSMO-UHFFFAOYAL
SMILES O=C(O)CC(O)(C(=O)O)CCC(=O)O
Properties
Chemical formula	C7H10O7
Molar mass	206.150 g·mol−1
Appearance	Colorless solid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

The molecule is related to citric acid by the addition of one methylene unit, hence the prefix "homo." Unlike citric acid, homocitric acid is chiral. The acid exists in equilibrium with the lactone.