Another aliquot from the protein digests was analyzed online
by high-performance liquid chromatography (HPLC)–electrospray
ionization (ESI)–ion trap (IT)–tandem MS (MS/MS) using a Spectra-
System P4000 liquid chromatography system (Thermo-Finnigan,
San Jose, CA, USA) coupled to an LCQ Deca XP Plus IT mass spec-
trometer (Thermo-Finnigan) as described previously [52]. Off-line
analyses by nanoESI–IT were performed using an LCQ Deca XP Plus
ion trap mass spectrometer (Thermo-Finnigan) equipped with a
nanospray interface as described previously [52].