Fractionation of the fibroin of Bombyx mori with trypsin

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Abstract
Hydrolysis of a solution of fibroin with trypsin gives rise to a precipitate containing 90% of the protein nitrogen and to a mixture of short soluble peptides. If tryptic hydrolysis is carried out in a medium containing 6% of lithium thiocyanate no precipitation occurs, and the hydrolysate may be acidified and dialysed to give a solution of peptides of high molecular weight. Further hydrolysis of this fraction with chymotrypsin shows that it consists predominantly of long sequences of amino acid residues throughout which glycyl residues alternate with alanine, serine, valine and tyrosine residues. Such sequences make up almost 90% of the fibroin molecule. Amino acid analyses of the fractions obtained by enzymic hydrolysis are presented, and the distribution of the amino acids in fibroin is discussed.