Identification of the Photoaffinity-labeled Abscisic Acid Binding Proteins from Maize Root Microsome

ABA binding protein (ABA-BP) was solubilized with 0.2% (W/V) Triton X-100 from the microsomal membrane of maize root, with a specific binding activity of 0.56 pmol ABA/g FW. When ABA was cross-linked to its binding sites by irradiating the microsomal proteins with light of 330 nm after incubation with low levels of H(3)-(-/+)ABA, it was found that this kind of photoaffinity labeling was specific to ABA-BP. On PAGE and SDS-PAGE three major protein bands with molecular weights of 72 kD, 47 kD and 37 kD were found with high radioactivity.