COMPARISON OF THE STRUCTURES OF HUMAN FIBRONECTIN AND PLASMA COLD-INSOLUBLE GLOBULIN

Human amniotic fluid fibronectin and plasma fibronectin (cold-insoluble globulin) are indistinguishable immunologically and by amino acid composition. Cyanogen bromide and tryptic peptides also suggest substantial structural homology. Carbohydrate analysis has demonstrated additional saccharides in fibronectin and an overall increase in carbohydrate content relative to cold-insoluble globulin. Limited proteolytic cleavage of the 2 proteins indicates differences in primary structure or in conformation. Using affinity purified antibodies to cold-insoluble globulin, a glucosamine-labeled pronase-resistant component, probably proteoglycan, coprecipitated with fibronectin, suggesting an association between these 2 macromolecules in the connective tissue matrix.