Abstract
Summary: For the study of its combining sites with antibody, silk fibroin was prepared by solution in lithium bromide, followed by dialysis. The fibroin had a molecular weight of 50,000–60,000 and contained only a slight amount of contaminants by immunologic assay. The number of antigenic sites occupied by antibody at equivalence varied with the rabbit immune serum but in most cases ranged from 2.6 to 3.2. The peptides in the soluble fraction following chymotryptic hydrolysis of fibroin were able to produce essentially complete inhibition of the fibroin-rabbit-antifibroin precipitin reaction at a concentration of 130 to 160 μm N per ml. Dialyzable peptides possessed differential inhibitory activity as shown by testing fractions obtained by partition column chromatography.

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