Vitronectin (VTN)also known as complement S-protein, serum spreading factor and somatomedin B is a protein that in humans is encoded by the VTN gene. The protein encoded by this gene is a member of the pexin family. Vitronectin is an abundant glycoprotein found in serum and the extracellular matrix and promotes cell adhesion and spreading, inhibits the membrane-damaging effect of the terminal cytolytic complement pathway, and binds to several serpin serine protease inhibitors. Vitronectin is a 75 kDa glycoprotein, consisting of 459 amino acid residues. By use of high resolution fluorescence in situ hybridization (FISH), Fink et al. (1992) mapped the VTN gene to 17q11. The localization was confirmed by cohybridization with a centromere-specific alphoid probe. About one-third of the protein's molecular mass is composed of carbohydrates. It is a secreted protein and exists in either a single chain form or a clipped, two chain form held together by a disulfide bond. Vitronectin has been speculated to be involved in hemostasis and tumor malignancy.