Protein profile of silkworm midgut of fifth-instar day-3 larvae

Proteomic analysis was performed on the midgut of fifth-instar day-3 female silkworm (Bombyx mori, strain p50) larvae. Though silkworm genome analysis has not yet been completed, the Drosophila genome and silkworm expression sequence tag (EST) data were applied to the analysis of the midgut proteins in the database (DB) for identification. The spots, which were excised manually from two-dimensional electrophoresis (2-DE) gels, were treated with 4-vinylpyridine for alkylation. Each spot was analyzed by capillary high-performance liquid chromatography coupled with ion-trap mass spectrometry (MS) after proteolysis using a trypsin. Nearly 60% of the proteins analyzed by MS were identified. These included many kinds of cytoskeleton proteins, ATPase, and chaperonins.