Comparison of the structures of human fibronectin and plasma cold‐insoluble globulin

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Abstract
Human amniotic fluid fibronectin and plasma fibronectin (cold‐incoluble globulin) are indistinguishable both immunologically and by amino acid composition. Cyanogen bromide and tryptic peptides also suggest substantial structural homology. However, carbohydrate analysis has demonstrated additional saccharides in fibronectin and an overall increase in carbohydrate content relative to coldinsoluble globulin. Furthermore, limited proteolytic cleavage of the two proteins indicates differences in primary structure or in conformation. Using affinity‐purified antibodies to cold‐insoluble globulin, a glucosamine‐labeled pronaseresistant component, probably proteoglycan, was found to coprecipitate with fibronectin, suggesting an association between these two macromolecules in the connective tissue matrix.