Evaluation of the acid-cleavable isotope-coded affinity tag reagents: Application to camptothecin-treated cortical neurons

The new generation of isotope-coded affinity tag (ICAT) reagents have been evaluated by labeling an equimolar amount of bovine serum albumin (BSA) with ICAT-¹²C₉ and ICAT-¹³C₉, combining the mixtures, digesting them with trypsin and analyzing the digestate both by μRPLC-tandem MS and by matrix-assisted laser desorption ionization (MALDI) TOF/TOF MS. The use of ¹³C in place of ²H resulted in both of the labeled peptides having identical elution characteristics in a reversed-phase separation. This similarity in elution allows ICAT-labeled peptides to be effectively analyzed using a μRPLC-MALDI-MS strategy as well. All of the cysteinyl-containing tryptic peptides from BSA were identified with only a 10% variation in the relative abundance measurements between the light and heavy versions of each peptide. A facile method for the removal of contaminants that arise from the cleaved biotin moiety that otherwise interfere with downstream separations and MS analysis has also been developed. The new ICAT reagents were then applied to the analysis of a cortical neuron proteome sample to identify proteins regulated by the antitumor drug, camptothecin.