Figure 1

Schematic representation of the concept behind the new technology. A. The Ca²⁺-sensitive photoprotein aequorin in the active form. includes an apoprotein and a covalently bound prosthetic group (coelenterazine). When Ca²⁺ ions bind to three high-affinity sites (EF-hand type), aequorin undergoes an irreversible reaction, in which a photon is emitted. B. Translocation studies can be performed on aequorin-tagged proteins, thanks to the different [Ca²⁺] present in distinct subcellular compartments. An aequorin-tagged signalling protein (proteinX-Aeq, green/orange sticks) located in the cytosol (light blue) translocates, upon stimulation in a receptor dependent or independent manner, to the plasma membrane (dark blue), where [Ca²⁺] is at least 1 order of magnitude higher then the cytosol, giving rise to an easily detectable increase in light emission (yellow flashes).