Abstract
Crystalline-region peptides (Cp) of silk fibroin were prepared by α-chymotryptic digestion from the large subunit of fibroin, which was prepared from the posterior silk glands of Bombyx mori with cold 30% ethanol treatment. The ratio of crystalline to amorphous regions in the large subunit was about 55 to 45 in terms of amino acid residues. Sephadex G-50 gel filtration gave a single peak with a slight shoulder, indicating the molecular size of Cp lies within a fairly limited range. On the other hand, elution profile of Cp from a column of DEAE-Sephadex A-50 exhibited one main peak with a shoulder and three minor peaks. This result shows the heterogeneity of Cp peptides in respect to their electrostatic charges. Amino acid analysis of these peptide fractions also supports this opinion. Molecular weight of Cp was estimated to be about 3900-4100 from terminal analyses and amino acid composition.
