Photoproteins as luminescent labels in binding assays

Certain marine organisms produce calcium-activated photoproteins that allow them to emit light for a variety of purposes, such as defense, feeding, br eeding, etc. Even though there are many bioluminescent organisms in nature, only a few photoproteins have been isolated and characterized. The mechani sm of emission of light in the blue region is the result of an internal che mical reaction. Because there is no need for excitation through external ir radiation for the emission of bioluminescence. the signal produced has virt ually no background. This allows for the detection of the proteins at extre mely low levels, making these photoproteins attractive labels for analytica l applications. In that regard, the use of certain photoproteins, namely, a equorin, obelin, and the green fluorescent protein as labels in the design and development of binding assays for biomolecules has been reviewed. In ad dition, a related fluorescent photoprotein, the green fluorescent protein ( GFP), has been recently employed in bioanalysis. The use of GFP in binding assays is also discussed in this review.