In the preceding paper the results of electron microscopic examination on the precipitates Fcp and Fcplx are reported. The former was obtained from the aqueous solution of silk fibroin (bombyx mori) hydrolyzed by chymotrypsin, the later being obtained when the former was dissolved in cupri-ethylenediamine and dialyzed. Fcp and Fcplx showed the structures of beta-fibroin and alpha-fibroin, respectively.
To examin further the structure of alpha-fibroin, the sedimented mat of Fcp 1x was prepared and submited to the X-ray diffraction measurements.
A clear fiber diagram was not obtained from X-ray diffraction pattern of a Fcp 1x mat, but were led to assign the following rectangular unit cell to the alpha-fibroin: a=4.59 A (direction of hydrogen bonding), b=7.20 A, c=9.08 A (fiber axis), This unit cell includes one polypeptide chain and the polypeptide molecule may take a helical conformation of four-fold, where the residue translation should be 2.27 A.
X-ray diffraction photographs of the mat of Fcp 1x and thin film adilute (0.1%) solution of regenerated silk fibroin shows long periods beginning with a spacing of 48.2 A as well as the ordinaly periods. At the present moment no definite relationship between the two kinds of the period is found. One plausible explanation would be that the log periods are caused by the globular structure formed by folded molecules.
Infrared absoption spectra indicates the existence of beta-structure for the Fcp. In Fcp 1x, no sign of the presence of alpha-helix is detected, but the feature of the spectra is close to that of the random coil structure.