A protein known to chemists for its bright blue fluorescence may not be fluorescent after all. Instead, it gives off light by a mechanism similar to that of light-emitting diodes (LEDs), chemists report. The finding suggests that some of the oceans' many bioluminescent animals may have been using the principle behind LEDs for millions of years.
The protein, antibody EP2-19G2, works in concert with an artificial organic molecule called stilbene, and is often used to label DNA molecules and to detect mercury contamination. Stilbene likes to lodge in a cozy hollow within the antibody's structure. When ultraviolet rays strike, they excite one of stilbene's electrons. In its free form, stilbene would then release its extra energy by letting a ring-shaped arm spin. But if stilbene is locked into place inside the antibody, it will instead release the energy by giving off a blue photon.
Scientists had assumed that this was banal fluorescence—an excited electron releasing