Isotope‐Labeled Photoaffinity Reagents and Mass Spectrometry To Identify Protein–Ligand Interactions

The target proteins of bioactive low-molecular-weight ligands can be discovered by the use of multifunctional photoaffinity labels in combination with mass spectrometry. The reagents contain a biotin label for affinity purification of the protein–ligand complex and a stable isotope label to facilitate its mass spectrometric identification (see scheme).