Some amino acid sequences in the amorphous fraction of the fibroin of Bombyx mori.

When an aqueous solution of the fibroin of Bombyx mori is treated with chymotrypsin, a white precipitate is formed that contains approximately 60% of the nitrogen of the original fibroin, and the remaining 40% of the nitrogen remains in solution in the form of a mixture of water-soluble peptides. These two fractions, the precipitate and the mixture of soluble peptides, we propose to call fraction Cp and fraction Cs respectively, and these terms replace our earlier nomenclature CTP and CTL, which is no longer acceptable because the former has become the standard abbreviation for cytidine triphosphate. The new system has the advantage that it is applicable by analogy to the fractionation of fibroin by other enzymes: tryptic hydrolysis thus gives rise to fractions Tp and Ts, peptic hydrolysis to fEractions Pp and Ps. The precipitate, fraction Cp, is composed almost entirely of glycine, alanine, and serine, has a molecular weight of about 4000, and has a sequence that can be represented by