This thesis deals with the potential role of the carbohydrate of human fibrinogen in its hepatic catabolism. First, the primary structure of carbohydrate in human fibrinogen was studied. The structural information was used to investigate the interaction of the asialo-glycopeptides from fibrinogen with the galactose/galactosamine lectin of mammalian liver By compositional analysis, all the carbohydrate on the parent molecule could be accounted for on the B(beta) and (gamma) chains. The 300-MHz PMR spectra of glycopeptides prepared from fibrinogen, B(beta) and (gamma) chains were all consistent with biantennary type oligosaccharide structures. This was confirmed by sequential digestion with exoglycosidases, and examining the products by 300-MHz PMR spectroscopy. Greater than 95% of the intact glycopeptide bound to Concanavalin A-Sepharose. These data were corroborated by methylation analysis to support the following structure (+OR-)NeuAc(alpha)(2,6)Gal(beta)(1,4)GlcNAc(beta)(1,2)Man(alpha)(1,3) Man(beta)(1,4)GlcNAc(beta)(1,4)GlcNAc(beta)1 - Asn (+OR-)NeuAc(alpha)(2,6)Gal(beta)(1,4)GlcNAc(beta)(1,2)Man(alpha)(1,6) To understand the behavior of desialylated fibrinogen in its hepatic catabolism, the relationship between oligosaccharide structure and binding affinity to the hepatic lectin was studied using both synthetic and naturally occurring neuraminyl-lactosamine carbohydrates. Inhibition of ('125)I-Tyr-asialo-triantennary glycopeptides binding to the surface of rabbit hepatocytes by carbohydrates, increased exponentially with the number of galactose residues per cluster. The estimated dissociation constants for ligands with one (mono-), two (bi-), three (tri), and four (tetra) galactose residues per cluster were 1 x 10('-3), 1 x 10('-6), 5 x 10('-8), and 1 x 10('-9), respectively. The uptake and degradation of asialo-biantennary and triantennary glycopeptides by isolated rabbit hepatocytes, maintained as monolayers, were studied. Both ligands were bound and internalized by the isolated hepatocytes. However, only in the case of asialo-triantennary glycopeptides was there detectable degradation. Parallel studies with ('125)I-asialoorosomucoid demonstrated binding, internalization, and eventual degradation of 95% of the added ligand. Further studies, in hepatocytes as monolayers and in perfused liver, yielded evidence for a pathway for glycopeptides which bypasses the lysosomal system. The implications of this nondegradative pathway in lysosomal homing, receptor mediated endocytosis and exocytosis were discussed
