Synthesis and resorption of a humoral chymotrypsin inhibitor, CI-8, by fat body of the silkworm, Bombyx mori.

The Bombyx mori hemolymph contains up to 16 chymotrypsin inhibitors (CIs). The present in vitro culture of tissues in Grace's medium indicated that CI-8, which belongs to the largest molecular-size group of CIs with sugar moiety, is synthesized in the fat body and secreted from it during the feeding period. When the fat body from other strain which synthesizes an allelic component (CI-7) instead of CI-8 was incubated in vitro in hemolymph from the strain which has CI-8, the fat body was found to receive CI-8. Thus it was concluded that CI-8, once secreted into the hemolymph, was again sequestered into the fat body after the onset of spinning. Protein granules isolated from the pupal fat body were shown to contain CI-8, indicating that the sequestered CI-8 is present in the protein granules.