[43,44]. Additionally,
the inability to remove the biotin moiety from target protein adducts
makes mass spectrometry analyses of isolated proteins difficult. This occurs
because the biotin appendage alters MS/MS fragmentation patterns
and prevents the identification of peptide adduction sites [44,49]. In
order to reduce high background proteins in proteomic adduct inventories,
it was necessary to synthesize a biotin linker that could be easily released
from target protein adducts to improve MS/MS identification of
adducted proteins. A newly synthesized click reagent containing azido
and biotin groups separated by a photocleavable linker improves upon
these preliminary affinity purification studies and allows the isolation of
a protein mixture enriched in adducted proteins (Fig. 4) [50]. Importantly,
by removing the biotinmoiety, this approach allowed the LC–MS/MS detection
of specific modification sites on proteins. Thus, such affinity
purification-photorelease strategies improve the capability to isolate
and identify specific lipid electrophile modifications to proteins from
complex biological mixtures.