Upon exposure to ultraviolet light, they are activated and covalently bind to interacting proteins that are within a few angstroms of the photo-reactive amino acid analog.
L-Photo-leucine and L-photo-methionine are analogs of the naturally occurring L-leucine and L-methionine amino acids that are endogenously incorporated into the primary sequence of proteins during synthesis using the normal translation machinery.
When used in combination with limiting media that is devoid of leucine and methionine, the photo-activatable derivatives are treated like naturally occurring amino acids by the cellular protein synthesis machinery.
Photo-leucine and photo-methionine derivatives contain diazirine rings that are activated when exposed to UV light to become reactive intermediates that form covalent bonds with nearby protein side chains and backbones.
Crosslinked protein complexes can be detected by decreased mobility on SDS-PAGE followed by Western blotting, size exclusion chromatography, sucrose density gradient sedimentation or mass spectrometry.