(1R,2S)-1-hydroxypropane-1,2,3-tricarboxylate 1-epimerase

Reaction catalyzed by isocitrate epimerase (D-threo-isocitrate = D-erythro-isocitrate)
Isocitrate epimerase
EC no.
CAS no.81210-68-6
IntEnzIntEnz view
ExPASyNiceZyme view
MetaCycmetabolic pathway
PDB structuresRCSB PDB PDBe PDBsum
Gene OntologyAmiGO / QuickGO


In enzymology, an isocitrate epimerase is classified by the EC number: This number indicates that it is an isomerase (5), specifically a racemase or epimerase (5.1) that acts on hydroxy acids and derivatives (5.1.2) of isocitrate ([1] Isocitrate epimerase specifically catalyzes the reversible reaction (image to the right, and written below):[2]


Isocitrate epimerase was originally isolated from the fungal cell-free extract of Penicillium purpurogenum [3], where it was discovered due to the excess accumulation of L-alloisocitric acid (D-erythro-isocitrate)—a diastereomer of isocitrate previously not seen in nature. In order to accumulate L-alloisocitric acid as a fermentation product, P. purpurogenum needed to be grown on citrate supplemented nutrient agar.[3][4] During this fermentation it was found that the fermentation yield of L-alloisocitric acid was capable of “exceeding 70% without producing any other stereoisomers of isocitiric acid or other metabolites”.[3]

This enzyme has not been heavily studied since first being identified in 1982, as a result of this there is presently not a crystal structure or active site description for isocitrate epimerase. Other isocitrate enzymes, such as isocitrate lyase and isocitrate dehydrogenase have been studied more closely due to their key roles in glycolysis and the TCA cycle.


  1. ^ "BRENDA - Information on EC - isocitrate epimerase". www.brenda-enzymes.org. Retrieved 2021-10-22.
  2. ^ "KEGG REACTION: R02318". www.genome.jp. Retrieved 2021-10-22.
  3. ^ a b c Hoshiko S, Kunimoto Y, Arima K, Beppu T (January 1982). "Mechanism of L-Alloisocitric Acid Fermentation: Isocitrate Epimerase Activity in the Cell-free Extract of Penicillium purpurogenum". Agricultural and Biological Chemistry. 46 (1): 143–151. doi:10.1080/00021369.1982.10865025. ISSN 0002-1369.
  4. ^ Beppu T, Abe S, Sakaguchi K (December 2004). "Accumulation of allo-isocitric acid by a Penicillium strain". The Journal of General and Applied Microbiology. 50 (6): 345–352. PMID 15965889.