Analysis of electrophoretic patterns of soluble proteins and trypsin inhibitors associated with the morphological changes of silk gland of Bombyx mori

Abstract

Developing of the material for the medical treatment using the silk protein of silkworm, Bombyx mori and the try of the collection of human proteins synthesized in the body of Bombyx mori through the silk gland is performed in recent years. Analyzing the changes of the soluble proteins included in the silk gland becomes more important. In this study, we evaluated the changes in soluble proteins and trypsin inhibitors in the silk gland of Bombyx mori. The concentration of soluble proteins increased with the growth of the silk gland, showed a plateau between the second half of the fifth larval instar and ripening stage, and rapidly decreased after ripening. The changes in the kinds of soluble proteins with the growth of the silk gland were examined in the posterior and middle parts of the silk gland by polyacrylamide gel electrophoresis. In the posterior area, proteins with various molecular weights were observed in all stages, and increased with the growth of the silk gland, while in the middle part, proteins with middle molecular weights were reduced with the growth and enlargement of the silk gland. The fractions of protein I (370kDa) and IV (22.5kDa) increased and decreased during the larval stage, but the protein IV alone remained in the ripening stage. These results suggested that various proteins produced in the posterior part of the silk gland accumulated as insoluble fibroin in the middle part of the silk gland. In the anterior segment of the middle part of the silk gland, trypsin inhibitors were observed from the end of the larval stage to the ripening stage. In the same ripening stage, protein II (230kDa) was observed. These findings suggested that trypsin-like proteinases and their inhibitors relate to the transformation of fibroin structure and silk line formation.