text: Traditionally, the recognition of protein-protein interactions was carried out through chemical cross-linking, that involved the use of moderately reactive bifunctional reagent, commonly attached to free amino groups. However, photochemical cross-linking is much more specific due to the short lifetime of the excited intermediates. In addition, photochemical cross-linking does not interfere with the antibodies recognition whilst the former does.
  But photo-leucines advantages go further, because in addition to having a lot of advantages, it doesnt have negative effects. For example, although unnatural amino acids are in general toxic to cells, photo-leucine has been proved not to have any substantial effect to cell viability. Those results have been corroborate by many experiments. For example, an essay with Escherichia coli-galactosidase showed that the addition of either of the three photo-amino acids or of a mixture of them had no effect on enzyme activity. That helps to conclude that photo-amino acids are nontoxic to cultivated mammalian cells and can, at least partially, functionally replace their natural forms.
  However, currently photo-reactive amino acids are used in combination with chemical cross-linkers in order to achieve the most reliable results possible within protein-protein interaction studies.