Precursor of the major egg-yolk proteins that are sources of nutrients during early development of oviparous organisms. Phosvitin is believed to be of importance in sequestering calcium, iron and other cations for the developing embryo. After incorporation from serum via a specific receptor, it is cleaved into four fragments, heavy and light chain lipovitellins, phosphovitin and YGP40, and YGP40 is released into the yolk plasma before or during compartmentation of lipovitellin-phosvitin complex into the yolk granule. By steroids (estrogen). Phosvitin, an egg yolk storage protein, is one of the most highly phosphorylated (10%) proteins in nature. Cathepsin D is responsible for intraoocytic processing of vitellogenin. May contain intrachain disulfide bonds. Vitellogenin II is the most abundant of the three vitellogenins (I, II, and III).