Ca(2+)-dependent bioluminescence photoprotein. Displays an emission peak at 470 nm (blue light). Trace amounts of calcium ion trigger the intramolecular oxidation of the chromophore, coelenterazine into coelenteramide and CO(2) with the concomitant emission of light. The reduction of the disulfide bond is necessary to regenerate aequorin from apoaequorin. Aequorin is used as an intracellular Ca(2+) indicator. Aequorin has a number of advantages over other Ca(2+) indicators, for example, low leakage rate from cells, lack of intracellular compartmentalization or sequestration and it does not disrupt cell functions or embryo development. Belongs to the aequorin family. Was originally thought to have an internal disulfide bond. Aequorin entry