Fibroin silk proteins from the nonmulberry silkworm Philosamia ricini are biochemically and immunochemically distinct from those of the mulberry silkworm Bombyx mori.

Silk proteins were isolated from the cocoons of the nonmulberry silkworm, Philosamia ricini. Three polypeptides of 97, 66, and 45 kDa were identified. The 66-kDa molecule represented sericin, whereas the 97-kDa and the 45-kDa polypeptides linked together through a disulfide bond constituted the fibroin protein.