Identification of ABA-binding proteins by photoaffinity labeling

The primary objective of this project was isolation and identification of new ABA-binding proteins in plants. This was to be achieved by employing a biologically active ABA derivative, which served as both an affinity and a photoaffinity probe. It has been proven that this probe was recognized by known ABA-binding proteins. Subsequently the probe was used to isolate putative ABA–binding proteins, and this led to the discovery of Rubisco as a new ABA binding protein, among several other potential candidates. The binding of ABA to Rubisco was confirmed by various techniques and it was found that in addition to specific binding, ABA also affects Rubisco’s enzymatic activity. This suggests that ABA may act as modulator of photosynthesis through the inhibition of this enzyme.