Vitonin (VTN), a member of the aggrecan family, is abundantly present in serum, extracellular matrix, and bone. It is a secreted protein that exists as a single chain or in a clamped, double-chained form formed by disulfide bonds.VTN contains three structural domains: an N-terminal growth regulator B structural domain, a central structural domain with homology to heme, and a C-terminal structural domain.VTN promotes cell adhesion and spreading, inhibits membrane disruption of the complement pathway in terminal cells, and binds to a variety of serine protease inhibitors. It is hypothesized to be associated with hemostasis, cell migration, and malignancy.