Proteolytic activity in the fat body during the pupal-adult metamorphosis of the silkworm,Bombyx mori

Abstract

Proteolytic activity with an optimum pH of 4.0 was found in fat bodies of 5 to 6 day-old female pupae of the silkworm, Bombyx mori, using azocoll as a synthetic substrate. The activity was strongly inhibited by p-chloromercuric benzoate at 0.5 mM, although inhibitory effect of several kinds of compounds on proteolytic activity was examined. Developmental changes in the activity were associated with two peaks of proteolytic activity related to the larval-pupal and pupal-adult transformation, the activity in the fat body of females was clearly higher than that of males. The profile of the proteolytic activity after chromatography on a column of Sephacryl S-300 showed that, in the female fat body, the highest activity was in the fraction with a molecular weight of about 232,000 daltons while, in male fat body, the highest activity was in the fraction with a molecular weight of about 105,000 daltons. The storage proteins were digested when extracts from fat bodies, which contain storage proteins and proteases, were incubated and only when the pH of the extract was adjusted to 4.0. In the case of female fat body, storage protein 1 was degraded earlier than storage protein 2. Furthermore, the administration of 20-hydroxyecdysone (5 μg/animal) to the isolated abdomens of female pupae (dauer-pupae) induced the proteolytic activity in the fat body in parallel with ovarian development. These results suggest that the proteases in female and male fat bodies are responsible for the utilization of storage proteins during pupal-adult development.