Isolation and characterization of surface glycopeptides from adult rat hepatocytes in an established line

Pericellular glycoconjugates of cultured fibroblasts from control and cystic fibrosis patients

1. Labeled glycoconjugates released by trypsin from cell surfaces of control and cystic fibrosis (CF) skin fibroblasts were purified and fractionated by column chromatography on Sephadex G-50 and Concanavalin A Sepharose. Based on chemical analysis and specific enzymatic digestions: (1) Glycoconjugates were characterized as O-linked glycopeptides consisting predominantly of glycosaminoglycan type and N-linked glycopeptides with glycans of complex type. Their relative proportions were similar between the two groups. (2) The N-linked glycopeptides exhibited an increased molar ratio of fucose to galactose in CF fibroblasts. (3) When pericellular glycoconjugates were metabolically labeled with [14C]glucosamine and [3H]fucose, incorporation and degradation kinetics were similar between the two groups.

The effect of a "bisecting" N-acetylglucosaminyl group on the binding of biantennary, complex oligosaccharides to concanavalin A, Phaseolus vulgaris erythroagglutinin (E-PHA), and Ricinus communis agglutinin (RCA-120) immobilized on agarose

The effect of a "bisecting" 2-acetamido-2-deoxy-beta-D-glucopyranosyl group, linked (1----4) to the beta-D-mannopyranosyl group of asparagine-linked complex and hybrid oligosaccharides, on the binding of [14C]acetylated glycopeptides to columns of immobilized concanavalin A (Con A), Phaseolus vulgaris erythroagglutinin (E-PHA), and Ricinus communis agglutinin-120 (RCA-120) was investigated. The presence of this "bisecting" GlcNAc group caused significant inhibition of the binding to ConA-agarose of biantennary complex glycopeptides in which the two branches are terminated at their nonreducing ends by two GlcNAc groups, or by a Gal and a GlcNAc group, or by two Gal groups, or by a Man and a GlcNAc group. Binding of biantennary, complex glycopeptides to E-PHA-agarose required a "bisecting" GlcNAc group, a Gal group at the nonreducing terminus of the alpha-D-Man-p-(1----6) branch, and a terminal or internal GlcNAc residue linked beta-(1----2) to the alpha-D-Manp-(1----3) branch. Binding to RCA-120-agarose occurred only when at least one nonreducing terminal Gal group was present, and increased as the proportion of terminal Gal groups increased; the presence of a "bisecting" GlcNAc group caused either enhancement or inhibition of these binding patterns. It is concluded that a "bisecting" GlcNAc group affects the binding of glycopeptides to all three lectin columns.

The presence of glycosylated, biologically active chorionic gonadotropin in human liver

Whole extracts of normal human liver contain hCG-like material as determined by radioimmunoassay using antibodies to the beta subunit of the hormone. However, the extracts are biologically inactive, when analyzed by the in vitro rat Leydig cell assay for steroidogenesis. When subjected to Concanavalin-A-Sepharose chromatography, the radioimmunoassayable material was entirely lectin-bound. After elution with methyl-alpha-D-glucopyranoside, the lectin-bound fractions now displayed biological activity.

Comparative study of the carbohydrate moieties of normal and pathological human immunoglobulins M

The well-known heterogeneity of normal and pathological immunoglobulins M was investigated in a study involving the characterization of their carbohydrate moieties. Oligosaccharide units were released from the native molecule by hydrazinolysis, and they were fractionated by affinity chromatography on a concanavalin A-Sepharose column to yield separate N-acetyl-lactosaminic-type and oligomannosidic-type structures. Further identification of these oligosaccharides was attempted by t.l.c. on silica gel and by determination of their monosaccharide compositions. A comparative study of the oligosaccharide units belonging to each population of immunoglobulin M was possible. Similarities were found in the occurrence of both types of oligosaccharide structures, and, in addition, a common double heterogeneity could be demonstrated for N-acetyl-lactosaminic-type structures: they could be resolved by affinity chromatography into bi-, tri- and tetra-antennary structures, and they also showed differences in N-acetylneuraminic acid content. Though some variations were observed in the exact composition of the oligosaccharide units within each population, it was possible to consider a representative oligosaccharide-unit composition of normal immunoglobulin M as a standard for comparison. On this basis a predominance of multi-antennary structures was observed in the more glycosylated pathological immunoglobulins M (10% carbohydrate content), whereas oligomannosidic structures were increased in pathological immunoglobulins M with a lower content of carbohydrates (7%). These variations are thought to reflect differences in the biosynthetic processing pathway of the carbohydrate units of the pathological immunoglobulins M or the enhanced expression of a molecular clone.

Structure determination by 360-MHz 1H-NMR spectroscopy and methylation analysis of a biantennary glycan of the N-acetyllactosaminic type isolated from rat-liver plasma membrane

Glycopeptides obtained by exhaustive pronase digestion of delipidated rat liver plasmic membranes were purified by gel filtration on Sephadex G-25. These glycopeptides were further fractionated by affinity chromatography on a concanavalin-A--Sepharose 4B column into the following fractions: (a) glycopeptides which did not bind to the column (fraction 1); (b) glycopeptides with weak affinity for concanavalin-A--Sepharose, which could be eluted with buffer only (fraction 2); (c) glycopeptides retained on the column and which could be eluted specifically with buffer containing 0.2 M methyl alpha-glucoside (fraction 3). On the basis of the carbohydrate composition, methylation analysis and 360-MHz 1H-NMR spectroscopy, the following primary structure of a glycan in fraction 2 is proposed: (see formula in text).

Membrane characteristics of adult rat liver parenchymal cells in primary monolayer culture

Parenchymal cells, isolated from normal adult rat liver (3 x 10(7) cells/g liver) by collagenase perfusion and maintained in nondividing monolayer culture, were employed to investigate cell surface properties of hepatocytes. Membrane transport systems for asialoorosomucoid (A-OM) and methotrexate (MTX) were lost rapidly in culture, whereas induction of tyrosine aminotransferase and transport of alpha-aminoisobutyrate actually increased during the first 3 days. Alterations in the membrane transport systems for A-OM and MTX reflected more generalized modifications of cell surface components induced during primary culture. Thus, the binding of concanavalin A(Con A) and wheat germ agglutinin (WGA) to cultured hepatocytes increased approximately 2-fold between 24 and 96 hr, and the incorportion of radioactive mannose and glucosamine into trichloroacetic acid-insoluble proteins increased 13-fold and 4-fold, respectively. Plasma membranes were isolated from cultured hepatocytes and the major structural proteins and glycoproteins were analyzed by SDS-polyacrylamide gel electrophoresis. Membrane instability between 24 and 96 hr of culture was characterized by time-dependent alterations in specific polypeptides and extensive changes in Con A- and WGA-binding glycoproteins. Although addition of a complex hormone supplement to the medium increased the number of viable cells and sustained A-OM and MTX transport systems for 24 hr, it had no influence on the altered membrane protein and glycoprotein profiles observed in its absence.

Methylation analysis in glycoprotein chemistry. General procedure for quantification of the products of solvolysis of permethylated glycopeptides and glycoproteins

A technique for the gas chromatographic analysis of the products of solvolysis of permethylated glycopeptides and glycoproteins has been developed. It involves methanolysis of a permethylated compound, quantitative transformation of methyl ethers of methyl glycosides into the corresponding O-trimethylsilyl(TMS)-O-methylalditols [2-deoxy-2-(N-methyl)acetamido-O-TMS-O-methylalditols in the case of hexosamine derivatives] and gas chromatographic quantification using a single column packed with 0.4% OV-225 on surface-modified Chromosorb.