Figure 3: MALDI-TOF/MS analysis of Keap1 reacted with MeHg. Recombinant Keap1 protein (0.25 μg/μL) was incubated for 30 min at 37°C with or without MeHg (10 μM). After the reaction, the Keap1 proteins were trypsinized and subjected to MALDI-TOF/MS analysis. Compared with the calculated mass of the unmodified peptides, the modified peptides P-1 to P-3 showed increased masses of 214 or 216 Da, corresponding to the addition of a single equivalent of MeHg.