Vitellin

Vitellin is a major phosphoprotein found in the yolk of egg cells, particularly in birds, reptiles, and fish. It serves as the primary source of nutrients for the developing embryo during its growth within the egg. Vitellin is synthesized in the liver of the female animal and transported to the ovary, where it is incorporated into the oocyte. Chemically, vitellin is a complex molecule composed of several polypeptide chains associated with lipids and phosphate groups. These components provide essential amino acids, fatty acids, and minerals required for embryonic development.

The structure of vitellin varies somewhat between species, but it generally exists as large macromolecular aggregates. In many vertebrates, vitellin is the primary stored form of nutrients in the egg yolk, though it is often referred to as vitellogenin when circulating in the blood before being taken up by the oocyte. Once inside the oocyte, vitellogenin is processed into vitellin. The breakdown of vitellin by enzymes within the developing embryo releases the stored nutrients, fueling metabolic processes and growth. The amount of vitellin present in an egg is a significant factor in determining the size and viability of the resulting offspring.