The synthesis of hemolymph proteins by the larval fat body of an insect Calpodes ethlius (Lepidoptera: Hesperiidae)

Abstract

Sheets of the fat body from fifth instar larvae of Calpodes ethlius (Lepidoptera: Hesperiidae) were incubated in artificial hemolymph in the presence of [ 35S]methionine to investigate protein synthesis and secretion. [ 35S]methionine was also injected into whole larvae to determine the nature and number of all the hemolymph proteins being made at this time. The fat body synthesizes and secretes at least 20 polypeptides into the medium. The fat body secretes 14 out of 26 detectable hemolymph polypeptides, amounting to about 90% of the total protein. About 12 polypeptides, amounting to 10% of the total hemolymph protein, are not contributed by the fat body. Antibodies made against whole hemolymph recognized at least 11 polypeptides secreted by the fat body as observed on fluorograms of immunoprecipitates. Arylphorin is secreted by the fat body into the medium. Arylphorin synthesized in vitro has been identified through its precipitation by antibodies to hemolymph arylphorin in the fat body and medium. Only arylphorin is so far unique in being secreted by more than one tissue and the synthesis of arylphorin by other tissues in Calpodes is therefore not related to a decline in arylphorin synthesis by the fat body.