Structure and synthesis of vitellogenin and vitellin from Calliphora erythrocephala

Egg extract of the blowfly, Calliphora erythrocephala, when analyzed by pore limit gradient acrylamide gel electrophoresis, was found to contain a major protein of mol. wt 210,000. A protein with the same mobility occurs in female, but not male haemolymph. The egg and haemolymph components were shown by immunochemical techniques to be female-specific, and are identified as the vitellin and vitellogenin, respectively. Under denaturing conditions, the egg extract yielded three major polypeptides of mol. wts 51,000, 49,000 and 46,000 (51, 49 and 46 K). The major 49 and 46 K polypeptides were shown to be subunits of the vitellin, while the 51 K and a presumably distinct 49 K polypeptide were found to be components of egg protein that forms a smear on polyacrylamide gels. Fat body cultured in vitro with [35S]-methionine synthesized and secreted the 49 and 46 K vitellin polypeptides, while the ovary appeared to synthesize 51 and 49 K polypeptides. We infer that the vitellin of C. erythrocephala is an oligomer, probably a tetramer, of the 49 and 46 K polypeptides which are synthesized by the fat body and secreted without major processing. Less abundant 51 and 49 K polypeptides found in the egg extract appear to be synthesized in the ovary.