EC - (S)-8-oxocitronellyl enol synthase

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IntEnz Enzyme Nomenclature


Accepted name:
(S)-8-oxocitronellyl enol synthase
Other name:
iridoid synthase [incorrect]
Systematic name:
(S)-8-oxocitronellyl enol:NAD(P)+ oxidoreductase



Isolated from the plants Catharanthus roseus, Olea europaea (common olive), and several Nepeta species. The enzyme reduces 8-oxogeranial, generating an unstable product that is subsequently cyclized into several possible products, either non-enzymically or by dedicated cyclases. The products, known as iridoids, are involved in the biosynthesis of many indole alkaloids. cf. EC, 7-epi-iridoid synthase.

Links to other databases

Enzymes and pathways: NC-IUBMB , BRENDA , ExplorEnz , ENZYME@ExPASy , KEGG , MetaCyc , UniPathway
Structural data: CSA , EC2PDB


  1. Geu-Flores, F., Sherden, N. H., Courdavault, V., Burlat, V., Glenn, W. S., Wu, C., Nims, E., Cui, Y., O'Connor, S. E.
    An alternative route to cyclic terpenes by reductive cyclization in iridoid biosynthesis.
    Nature 492 : 138-142 (2012). [PMID: 23172143]
  2. Hu, Y., Liu, W., Malwal, S. R., Zheng, Y., Feng, X., Ko, T. P., Chen, C. C., Xu, Z., Liu, M., Han, X., Gao, J., Oldfield, E., Guo, R. T.
    Structures of Iridoid Synthase from Cantharanthus roseus with Bound NAD(+) , NADPH, or NAD(+) /10-Oxogeranial: Reaction Mechanisms.
    Angew. Chem. Int. Ed. Engl. 54 : 15478-15482 (2015). [PMID: 26768532]
  3. Alagna, F., Geu-Flores, F., Kries, H., Panara, F., Baldoni, L., O'Connor, S. E., Osbourn, A.
    Identification and Characterization of the Iridoid Synthase Involved in Oleuropein Biosynthesis in Olive (Olea europaea) Fruits.
    J. Biol. Chem. 291 : 5542-5554 (2016). [PMID: 26709230]
  4. Qin, L., Zhu, Y., Ding, Z., Zhang, X., Ye, S., Zhang, R.
    Structure of iridoid synthase in complex with NADP(+)/8-oxogeranial reveals the structural basis of its substrate specificity.
    J. Struct. Biol. 194 : 224-230 (2016). [PMID: 26868105]
  5. Sherden, N. H., Lichman, B., Caputi, L., Zhao, D., Kamileen, M. O., Buell, C. R., O'Connor, S. E.
    Identification of iridoid synthases from Nepeta species: Iridoid cyclization does not determine nepetalactone stereochemistry.
    Phytochemistry 145 : 48-56 (2018). [PMID: 29091815]
  6. Lichman, B. R., Kamileen, M. O., Titchiner, G. R., Saalbach, G., Stevenson, C. E. M., Lawson, D. M., O'Connor, S. E.
    Uncoupled activation and cyclization in catmint reductive terpenoid biosynthesis.
    Nat. Chem. Biol. 15 : 71-79 (2019). [PMID: 30531909]
  7. Lichman, B. R., O'Connor, S. E., Kries, H.
    Biocatalytic Strategies towards [4+2] Cycloadditions.
    Chemistry 25 : 6864-6877 (2019). [PMID: 30664302]

[EC created 2013 as EC, part transferred 2019 to EC]