(a) Experiments
with isolated protein. Photoaffinity
labeling of recombinant CAIX after 30 min illumination with excess
ligand 5 and click with azide-fluor-488; the top gel
(black background) shows the fluorescence at 488 nm, and the one below
depicts protein staining with Coomassie Brilliant Blue (CBB) G250.
Competition with 6, which lacks a diazirine, suppresses
labeling with 5 (lanes 2 and 4). (b) Experiments
with MDA-MB-231 cell lysates. MDA-MB-231 cell lysate was
treated with PAL probe 5 under 365 nm illumination for
30 min and then clicked with biotin-azide. NeutrAvidin agarose was
used to pull down the biotinylated proteins, and the material captured
was run on a SDS-PAGE gel. Lane 1 shows staining of CAIX on the Western
blot image with a CAIX Ab, lane 2 shows sample pretreated with blocking
ligand 6, lane 3 shows no ligands, and lane 4 depicts
the lysate without PAL.