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. Belongs to the aequorin family. Was originally thought to have an internal disulfide bond.