Evidence for redox forms of the Aequorea green fluorescent protein.

Highly purified recombinant Aequorea green fluorescent protein is able to undergo a reversible oxidation-reduction reaction in the presence of molecular oxygen. In the oxidized form in near UV light, the protein is highly fluorescent, but when reduced with sodium dithionite, it becomes completely non-fluorescent. On exposure to molecular oxygen the reduced, non-fluorescent protein reverts to its original fluorescent state.