Aequorin emits light in the presence of Ca2+, decomposing into apoaequorin, coelenteramide and CO2. Semisynthetic aequorins, produced by replacing the coelenterazine moiety in aequorin with analogues of coelenterazine, showed widely different sensitivities to Ca2+ as well as certain spectral variations. A group of semisynthetic aequorins, e-type aequorins, showed bimodal luminescence, with peak...