Abstract
When aqueous solution of silk fibroin are acted on by chymotrypsin, a precipitate (Fcp) is formed. Its molecular weight is estimated at about 3, 000 by means of the titration of terminal amino acids. From the result of paperchromatography, it is ascertained that the Fcp is composed of the four amino acid residues of glycine, alanine, serine and tyrosine.
When the Fcp is dissolved in cupri-ethylenediamine and dialyzed, a white precipitate (Fcp 1×) of about 80 weight percent of the original Fcp is obtained again.
The X-ray powder diffraction patterns of the Fcp show that its structure is highly crystalline and resembles closely to the β-structure of fibroin proposed by ‘Shimizu’. The electron micrograph of the Fcp shows that small rod-shaped particles aggregate ramdomly. The X-ray diffraction patterns of the Fcp 1× resemble in α-structure of fibroin proposed by ‘Shimizu’ and show higher crystallinity than the Fcp. The electron micrograph of the Fcp 1× shows the spherulitic aggregates formed by the fibrillar single crystal.
From the reciprocal lattice patterns on xy-plane estimated from the selected area diffraction patterns, it may be expected that α-structure of fibroin is orthorhombic and has the dimensions, 7.20A, 4.49A and C-axis (chain axis) perpendicular to xy-plane. Selected area micrograph shows that the planes correspond to plane distance 7.20A and 4.49A are oriented parallel to and perpendicular to the fibrillar axis respectively.
