Preparation of undegraded native molecular fibroin solution from silkworm cocoons

The molecular mass of solubilized fibroin prepared from silk was analyzed by SDS-PAGE. It was found that the fibroin molecule was degraded during reeling, degumming (removal of sericin), and dissolution of silk threads. A protocol for the preparation of solubilized fibroin conserving its native molecular size is offered, that is, (1) to use only fresh cocoons (not dry cocoons or reeled silk threads), (2) to degum by heating in 8 M aqueous urea, and (3) to dissolve by saturated (∼9 M) aqueous lithium thiocyanate at room temperature.