Recombinant GSTP1a-1a samples incubated without (panel A) and with (panel B) a 20-fold molar excess of NO2-LA were prepared as described in Figure 9 and processed for mass spectrometry according to Experimental Procedures. Raw ion data were transformed by maximum entropy calculations to yield masses corresponding to unmodified GSTP1a monomers (23,223 [-met] and 23,354 [+met]) and to GSTP1a monomers adducted with one NO2-LA (23,548 [-met] and 23,679 [+met]) or two NO2-LA (23,873 [-met] and 24,004 [+met]) molecules.