Precursor of the egg-yolk proteins that are sources of nutrients during embryonic development. May supply aromatic amino acids to the cuticle of rapidly developing embryos. Produced by the fat body, where it is cleaved in the rough endoplasmic reticulum or cis-Golgi before being secreted into hemolymph. It is then sequestered by a single class of receptor mediated endocytosis in the ovary. Synthesized only by sexually mature female after ingestion of blood. Glycosylated, phosphorylated and sulfated. The large subunit is sulfated more extensively than the small one.