Studies on the Soluble Proteins of the Silk Gland of the Silkworm, Bombyx mori

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Abstract
The precursors of silk fibroin were extracted in sodium bicarbonate solution from the silk gland of the silkworm, Bombyx mori, and studied by ultracentrifugation. Three components (s ∼ 1.8, 1.5, and 1) were found, but there was insufficient evidence to show whether these were three different proteins, aggregates, or configurational variants. In solutions containing urea, only one component was detected. On standing, the viscosity increased and a fibrous gel formed. During this change the sedi mentation velocities decreased and the polydispersity increased. The mechanism of this change is discussed. The gland extract initially gave a silk I type x-ray pattern and after aging a silk II pattern. The other constituents of the fiber—sericin, pigments, and waxes—were also present in the gland. In the storage vessel the sericin surrounded the fibroin.