Calcium aequorin activation

Cormier, M. J., Prasher, D. C., Longinaru, M., and McCann, R. O. (1989). The enzymology and molecular biology of the calcium-activated photoprotein, aequorin. Photochem. Photobiol. 49 509-512. 

Mori K, Maki S, Niwa H, Ikeda H, Hirano T. Real light emitter in the bioluminescence of the calcium-activated photoproteins aequorin and obelin light emission from the singlet-excited state of coelenteramide phenolate anion in a contact ion pair. Tetrahedron 2006 62 6272-88. 

Kendall, J. M., et al. (1992). Engineering the Ca2+-activated photoprotein aequorin with reduced affinity for calcium. Biochem. Biophys. Res. Commun. 187 1091-1097. 

Obelin is a Ca2+-activated bioluminescent photoprotein that has been isolated from the marine polyp Obelia longissima. Binding of calcium ions determines a luminescent emission. The protein consists of 195 amino acid residues [264] and is composed of apoobelin, coelenterazine, and oxygen. As aequorin, it contains three EF-hand Ca2+-binding sites and the luminescent reaction may be the result of coelenterazine oxidation by way of an intramolecular reaction that produces coelenteramide, C02, and blue light. As for aequorin, the luminescent reaction of obelin is sensitive to calcium and the protein was used in the past as an intracellular Ca2+ indicator. More recently, the cloning of cDNA for apoobelin led to the use of recombinant obelin as a label in different analytical systems. 

The jellyfish Aequorea contains a photoprotein, which emits light only when calcium ions are present.672 673 Since light emission can be measured with great sensitivity (modern photomultipliers can be used to count light quanta) the protein aequorin and related photoproteins674a are used as a sensitive indicator of calcium ion concentration.674 (In a similar way the firefly luciferin-luciferase system, which requires ATP for activation, is widely used in an assay for ATP.)... 

High throughput flash luminescence readers such as the FDS6000 and 7000, as well as the Lumax Flash HT, enable functional GPCR and calcium channel testing. A sensitive photon-counting CCD camera enables aequorin and luciferase activity to be measured by flash luminescence. Thus, these advances allow fluorescence-based assays to be replaced by luminescence-based assays,... 

The activity of an enzyme is responsible for the glow of the luminescent jellyfish at left. The enzyme aequorin catalyzes the oxidation of a compound by oxygen in the presence of calcium to release CO2 and light. [(Left) Fred Bavendam/Peter Arnold.]... 

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