EC - Calcium-regulated photoprotein

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IntEnz Enzyme Nomenclature


Accepted name:
calcium-regulated photoprotein
Other names:
Ca2+-regulated photoprotein
calcium-activated photoprotein
Systematic name:
coelenterazine:oxygen 2-oxidoreductase (decarboxylating, calcium-dependent)



Ca2+-regulated photoproteins are found in a variety of bioluminescent marine organisms, mostly coelenterates, and are responsible for their light emission. The best studied enzyme is from the jellyfish Aequorea victoria. The enzyme tightly binds the imidazolopyrazinone derivative coelenterazine, which is then peroxidized by oxygen. The hydroperoxide is stably bound until three Ca2+ ions bind to the protein, inducing a structural change that results in the formation of a 1,2-dioxetan-3-one ring, followed by decarboxylation and generation of a protein-bound coelenteramide in an excited state. The calcium-bound protein-product complex is known as a blue fluorescent protein. In vivo the energy is transferred to a green fluorescent protein (GFP) by Förster resonance energy transfer. In vitro, in the absence of GFP, coelenteramide emits a photon of blue light while returning to its ground state.

Links to other databases

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


  1. Shimomura, O., Johnson, F. H., and Saiga, Y.
    Purification and properties of aequorin, a bio-(chemi-) luminescent protein from the jellyfish, Aequorea aequorea.
    Fed. Proc. 21: 401 (1962).
  2. Morise, H., Shimomura, O., Johnson, F. H., Winant, J.
    Intermolecular energy transfer in the bioluminescent system of Aequorea.
    Biochemistry 13: 2656-2662 (1974). [PMID: 4151620]
  3. Inouye, S., Noguchi, M., Sakaki, Y., Takagi, Y., Miyata, T., Iwanaga, S., Miyata, T., Tsuji, F. I.
    Cloning and sequence analysis of cDNA for the luminescent protein aequorin.
    Proc. Natl. Acad. Sci. U.S.A. 82: 3154-3158 (1985). [PMID: 3858813]
  4. Head, J. F., Inouye, S., Teranishi, K., Shimomura, O.
    The crystal structure of the photoprotein aequorin at 2.3 A resolution.
    Nature 405: 372-376 (2000). [PMID: 10830969]
  5. Deng, L., Vysotski, E. S., Markova, S. V., Liu, Z. J., Lee, J., Rose, J., Wang, B. C.
    All three Ca2+-binding loops of photoproteins bind calcium ions: the crystal structures of calcium-loaded apo-aequorin and apo-obelin.
    Protein Sci. 14: 663-675 (2005). [PMID: 15689515]

[EC created 2018]