The N- and O-linked carbohydrate chains of human, bovine and porcine plasminogen. Species specificity in relation to sialylation and fucosylation patterns

The structures of the N-and O-glycans of human, bovine and porcine plasminogen were determined by 500-MHz 1H-NMR spectroscopy. The N-glycans of all three species proved to be of the N-acetyllactosamine type differing from one another with respect to the sialylation and fucosylation patterns. In the N-glycan of human plasminogen the two antennae are sialylated with N-acetylneuraminic acid (NeuAc), whereas in the bovine counterpart both branches carry significant amounts of N-glycolylneuraminic acid (NeuGc). In porcine plasminogen the sialic acid is mainly NeuAc; the Manalpha1->6 branch, however, is only partially sialylated. In addition, the porcine N-glycan is fucosylated to about 80% in alpha1->6 linkage to the GlcNAc-1 residue. The O-glycans of the three species possess an identical Galbeta1->3GalNAc core which is alpha2->3 sialylated with NeuAc at Gal. The disialylated form, which is also present in all three species, has an additional NeuAc residue in alpha2->6 linkage to GalNAc. Mono-and disialylated forms occur in different molar ratios in the different plasminogens: 80:20 in human, 70:30 in bovine and 50:50 in porcine. This study on the carbohydrate moiety of these three plasminogens reveals species specificity in terms of various types of microheterogeneities

N-Terminal sequences of pig intestinal sucrase-isomaltase and pro-sucrase--isomaltase. Implications for the biosynthesis and membrane insertion of pro-sucrase--isomaltase

The hog sucrase—isomaltase complex is anchored to the small-intestinal brush border membrane, as in the rabbit, via a hydrophobic segment located in the N-terminal region of the isomaltase subunit. The immediate precursor of the ‘final’ sucrase—isomaltase (i.e., pro-sucrase—isomaltase as prepared from adult hogs whose pancreas had been disconnected from the duodenum) is an amphiphilic single polypeptide chain of M r 260 000–265 000. Its N-terminal sequence is virtually identical with (not merely homologous to) the corresponding region of the isomaltase subunit of ‘final’ sucrase-isomaltase. This shows that the isomaltase portion of pro-sucrase—isomaltase in the N-terminal ‘half’ of the precursor polypeptide chain. Thus the succession of domains in pro-sucrase—isomaltase and its mode of anchoring in the membrane could be deduced. On this basis a likely mechanism of biosynthesis and insertion is proposed