Precursor of the 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. Produced by the liver, secreted into the blood and then sequestered by receptor mediated endocytosis into growing oocytes, where it is generally cleaved, giving rise to the respective yolk components. 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.