Gel cores were washed twice with ultrapure H2O followed by two washes with CH3CN–H2O (1:1, v/v) 50 mM NH4HCO3, pH 8.0. After dehydration with CH3CN, cores were rehydrated in 10 ng/ll trypsin (Promega, Madison, WI) for 30 min at 4 C, followed by incubation at 37 C for 3 h. Peptides were extracted once with CH3- CN–H2O containing 0.1% CF3CO2H (1:1, v/v) by sonication for 15 min.