絹フィブロインの微細構造に関する研究

第4報　家蚕フィブロインのα型について

抄録

Silk fibroin of coagulated and dried silk gland of Bombyx mori L. shows an X-ray diagram of the so-called α form named by Shimizu.
When this silk gel is stretched up to 50%, the specific diffraction of 4.5 and 7.25A spacings begin to move to the meridian and to the equator respectively.
This fact seems to suggest that α-form is something like the cross-β-form, with its backbone spacing of 4.5A.
On LiBr silkfilms, it has been found that the unoriented cross-β-form (intra-chain β-form) shows the same diffraction pattern and infrared spectrum as the interchain β-form.
An inspection of the X-ray diffraction pattern of the silk gel revealed that the cross-β-form is not present in the gel.
When the film of LiBr silk fibroin which contains the α-form is drawn with polyvinyl alcohol as a plasticizer, the amide I band at 1660cm^-1 and amide II band at 1530cm^-1 showed perpendicular and parallel dichroism, respectively.
Therefore, the α-form is not a structure like that of the α-helix.
The structure of the α-form may possibly be similar to that of polyglycine II with its hydrogen bonds projected out perpendicularly to the polypeptide chain.