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Information on EC 1.13.12.24 - calcium-regulated photoprotein

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IUBMB Comments
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 Forster resonance energy transfer. In vitro, in the absence of GFP, coelenteramide emits a photon of blue light while returning to its ground state.
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The enzyme appears in viruses and cellular organisms
Reaction Schemes
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[apoaequorin]
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3
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[excited state blue fluorescent protein]
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Synonyms
aequorin, alcium-activated photoprotein, berovin, BFP-aq, blue fluorescent protein, Ca2+-regulated photoprotein, clytin, halistaurin, mitrocomin, mnemiopsin, more
REACTION
REACTION DIAGRAM
COMMENTARY hide
ORGANISM
UNIPROT
LITERATURE
[aequorin] + 3 Ca2+ = [aequorin] 1,2-dioxetan-3-one
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(1c)
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[aequorin] 1,2-dioxetan-3-one = [excited state blue fluorescent protein] + CO2
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(1d)
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[apoaequorin containing coelenterazine] + O2 = [aequorin]
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(1b)
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[apoaequorin] + coelenterazine + O2 + 3 Ca2+ = [excited state blue fluorescent protein] + CO2
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overall reaction
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[apoaequorin] + coelenterazine = [apoaequorin containing coelenterazine]
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(1a)
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