EC Explorer

1.13.12.24

calcium-regulated photoprotein

[apoaequorin] + coelenterazine + O₂ + 3 Ca²⁺ = [excited state blue fluorescent protein] + CO₂ (overall reaction);;(1a) [apoaequorin] + coelenterazine = [apoaequorin containing coelenterazine];;(1b) [apoaequorin containing coelenterazine] + O₂ = [aequorin];;(1c) [aequorin] + 3 Ca²⁺ = [aequorin] 1,2-dioxetan-3-one;;(1d) [aequorin] 1,2-dioxetan-3-one = [excited state blue fluorescent protein] + CO₂

Ca²⁺-regulated photoprotein, calcium-activated photoprotein, aequorin, obelin, halistaurin, mitrocomin, phialidin, clytin, mnemiopsin, berovin

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.

created 2018