The Amino Acid Composition of Bombyx mori Silk Fibroin and of Tussah Silk Fibroin

The structure of tussah silk fibroin (with a note on the structure of β-poly-L-alanine)

“…-3, the average residue weight is calculated to be about 71. This value is exactly the weight of an alanine residue, but is considerably smaller than the value 83.5 calculated for Tussah silk from the data of Schroeder & Kay (1955). Furthermore, the distance between adjacent pleated sheets, 5.3/~, is insufficient to accommodate the side chains of the larger aminoacid residues, such as tyrosine.…”

“…For X-ray photography, degummed fibers (Schroeder & Kay, 1955) were arranged in the form of a bundle about 0.5 ram. in diameter.…”

“…The agreement ~4th the observed intensities is seen to be quite satisfactory ; it could be improved by the application of an anisotropic temperature factor to take account of the apparent disorder in the c direction which is manifested by the diffuseness of the 001 reflections. It should be pointed out that the calculations included one flcarbon atom for each residue of the structure, whereas the results of chemical analysis of Tussah silk (Schroeder & Kay, 1955) …”

“…The work described in this article was carried out under a contract ) between the Office of Naval Research and the California Institute of Technology. Mean residue weight 78-3 83.5 * Calculated from the data of Schroeder & Kay (1955). insufficient to permit the occurrence of glycine as alternate residues along the polypeptide chains.…”

The Chemistry of Proteins and Peptides

“…The finding that Tussah silk fibroin, besides other sharp differences in the minor components, shows an inverted ratio of glycine and alanine residues suggests that the physical properties of silk are largely independent of the frequency of occurrence of the distinguishing methyl group (78). On the other hand, Braunitzer & Wolff (193) have recently investigated spider fibroin (Nephila madagascariensis) and found it remarkably similar to Bombyx mori fibroin, both in amino acid composition and in N-terminal residues; both types of fibroin contained a variety of end groups, amounting to only about 1 per 200,000 to 300,000 grams of protein.…”