Molecular characterization of an insect transferrin and its selective incorporation into eggs during oogenesis.

A protein with a molecular mass of 65 kDa that was specifically taken up into eggs was purified from the hemolymph of adult female Sarcophaga peregrina flies. From cDNA analysis, this protein was shown to be a Sarcophaga transferrin. Unlike mammalian transferrin, the similarity between its N-terminal and C-terminal halves was only 19%, and it was suggested to conjugate one iron atom/molecule in its N-terminal half. Sarcophaga transferrin was found to transport iron ions into eggs during oogenesis and deliver them to another protein, thought to be ferritin. No significant activation of the transferrin gene was detected during embryogenesis, so probably maternal transferrin is used as an intercellular or intracellular iron-transporter during embryogenesis of this insect.