Human Fibronectin Native Protein. Fibronectin is a disulfide-bonded dimer with a molecular weight range of 230-250 kDa. In the extracellular matrix of several connective tissues and vessels, fibronectin is present as an insoluble protein that is extensively cross-linked by interchain disulfide bonds forming high molecular mass polymers. Fibronectin is most abundant during embryonic development and tissue remodeling. Fibronectin is also present at high concentrations as a soluble plasma protein. Fibronectin is organized as a linear series of repeating modules which form domains for interaction with fibronectin itself, other matrix components (e.g. collagen and heparin) and receptors on cells (e.g. integrins). Fibronectin is present in a solu