Mixed isotope photoaffinity reagents

Mixed isotope photoaffinity reagents have been developed to facilitate target identification by mass spectrometry. To demonstrate the approach, cyclosporine was both biotinylated and functionalised with a mixed isotope pho-toactivatable benzophenone probe (Figure 1.8). Irradiation of the probe in the presence of a mixture of proteins led to selective cross-linking to cyclophilin A. The biotin tag enabled easy separation of the cross-linked protein from other proteins in the mixture. Subsequently, after tryptic digestion, the mixed isotope tag facilitated the identification, by mass spectrometry, of the peptides that were cross-linked to the functionalised probe. 

Figure 1.8 A mixed isotope photoaffinity reagent in which cyclosporine has been functionalised with both biotin and a photoactivatable benzophenone probe.

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