Fourteen of the separated bands which represented major globulin
subunits or polypeptides were manually excised from the gel
and the gel pieces were de-stained with 50 mM NH4HCO3 in 50%
(v/v) acetonitrile (ACN) and dried for 10 min with 100% ACN and
then under vacuum for 30 min. Gel pieces were rehydrated in
30 lL 50mM NH4HCO3 containing 30 ng/lL sequencing-grade
trypsin (Promega) and incubated for 1 h at 4 C. After brief centrifugation,
excess trypsin solution was removed and samples were
incubated at 37 C for 16 h. On the following day, 30 lL 50% (v/v)
ACN with 1% (v/v) formic acid was added to the gel pieces which
were incubated for 1 h at 37 C. The supernatant containing the
peptides was collected after brief centrifugation. This was repeated
once. The combined supernatant was dried under vacuum before
reconstituted in 20 lL 1% (v/v) formic acid.