Studies on Silk Fibroin of Bombyx mori Directly Extracted from the Silk Gland

III. N-Terminal Analysis and Degradation in a Slightly Alkaline Solution

Abstract

The N-terminal amino acids of fibroin directly extracted from the silk gland of Bombyx mori larva were examined by dinitrophenylation and dansylation. Quantitative analysis of the N-terminal amino acids revealed that Asp and Ser were liberated to the extent of one mole each per mole of fibroin. Glycine and alanine, which were dominant in fibroin and were previously reported as the N-terminal residues, were hardly detected. Further analysis showed that aspartate and serine were derived from the large component (C-I), which was connected with the small component (E-I) by disulfide bonds to form the fibroin molecule. The latter component gave no N-terminal residue. Fibroin was degraded in a slightly alkaline solution and reinvestigated by N-terminal analysis, gel electrophoresis, and sedimentation analysis. DFP inhibited this degradation and the presence of some proteolytic enzyme was indicated.