Abstract
Dissolved Bombyx mori fibroin was treated with 0.1 [image]-sodium hydroxide at 3[degree], and the rate of peptide-bond cleavage was measured, together with the fall in viscosity. Solutions of fibroin that had been treated with 0.1 [image]-sodium hydroxide at 3[degree] for 48 hr. were fractionated by means of the cationic dye rivanol (6,9-diamino-2-ethoxy-acridine lactate) and by the addition of saturated ammonium sulphate. The precipitated fractions, which represented about 10% of the total protein, were found to be substantially different in composition from the soluble fractions. They contained little glycine and had mean chain lengths of about 230 residues. The fractionation of fibroin by alkali is compared with that obtained by hydrolysis with trypsin, and the relation of the fractions to the fibroin molecule is discussed.

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