Physicochemical properties of some glycopeptides released from human erythrocyte membranes by trypsin

Contribution of glycoproteins to fibrinogen-induced aggregation of erythrocytes

The contribution of membrane glycoproteins to the velocity of fibrinogen-induced erythrocyte aggregation was examined using a rheoscope combined with a video camera, an image analyzer and a computer. The structure of glycoproteins was modified with proteolytic enzymes, trypsin or alpha-chymotrypsin. (1) Mild enzymatic treatment of erythrocytes decreased the velocity of erythrocyte aggregation, but more intense treatment increased the velocity remarkably. (2) The erythrocyte aggregation was affected not only by the density of surface negative charge of erythrocytes, but also by the structural changes of glycoproteins. (3) Erythrocyte deformability and the morphological characteristics were not altered by these enzymatic treatments. The physiological significance of glycoproteins of erythrocyte surface for the survival of erythrocytes and for the suspension stability of blood was discussed.

Comparative study on the main membrane-surface sialoglycopeptides released from young and old human erythrocytes with trypsin

1. The amount of sialoglycopeptide (SGP) mixture released from young (Y) erythrocytes by trypsin treatment was significantly larger than that from old (O) ones. 2. The two main membrane-surface sialoglycopeptides (Y-SGP and O-SGP) were isolated in yields of about 45% and 42% from the mixtures by a combination of Sephadex G-50 superfine gel filtration with DEAE-cellulose chromatography, respectively. Molecular weights of 12,000 and 12,100, respectively, were found for the Y-SGP and the O-SGP. 3. The Y-SGP showed a greater proportion of sialic acid than the O-SGP. The contents of galactose, N-acetylglucosamine and N-acetylgalactosamine of the Y-SGP were significantly lower than those of the O-SGP. 4. Both the SGPs exhibited the same reactivities against the MN reagents, but the reactivities against the lectins of Limulus polyphemus and Phaseolus vulgaris (E) were stronger in the Y-SGP than in the O-SGP. Neither the Y-SGP nor the O-SGP showed the reactivity to Arachis hypogaea (anti-T) lectin.

Glycophorins A, B, and C: a family of sialoglycoproteins. Isolation and preliminary characterization of trypsin derived peptides

Two new sialoglycoproteins, glycophorin B and glycophorin C, were isolated from erythrocyte membranes by extraction with lithium diiodosalicylate, partition in aqueous phenol, gel filtration in detergent, and preparative polyacrylamide gel electrophoresis in sodium dodecyl sulfate. The two proteins were characterized by amino acid and carbohydrate analysis, separation of tryptic peptides, and isolation and purification of the amino terminal glycopeptide from each polypeptide chain. Glycophorin B is found in two forms in electrophoretograms of normal erythrocyte membranes, corresponding to monomer and dimer, as has been similarly described for glycophorin A. By using antibodies to a carboxy terminal determinant of glycophorin A, and direct staining of gels with antibodies and 125I-protein A from Staph. aureus, as well as by two-dimensional immunoelectrophoreis, only the two known forms of glycophorin A are detectable. The data confirm and extend the notion that the sialoglycoproteins in human red cells are dimeric molecules which are either preformed in the membrane or which can readily be generated in vitro. Only glycophorin A and glycophorin C are sensitive to trypsin while in situ in the intact red blood cells.

Different N-terminal amino acids in the MN-glycoprotein from MM and NN erythrocytes

The major human erythrocyte membrane (MN-) sialoglycoprotein was purified from MM, MN and NN cells using detergent gel and ion exchange chromatography. N-terminal analyses with dansyl-chloride revealed serine in preparations from MM and leucine in those from NN erythrocytes, whereas glycoprotein isolated from MN cells contained both the above amino acids. These data strongly suggest that the above residues may represent the structural difference between the M and N antigens. Evidence was also obtained that the Ss-glycoprotein, which is associated with "N" activity, exhibits the same N-terminal amino acid (leucine) as the MN glycoprotein from NN cells.

Changes in carbohydrate content of surface membranes of human erythrocytes during ageing

The carbohydrate content (neutral hexoses, fucose, sialic acid, and hexosamine) of human erythrocytes is significantly higher in young than in old erythrocytes. The differences observed in the carbohydrate content of surface glycopeptides, obtained after incubation with either Pronase or trypsin, is still more striking, suggesting important modifications of the carbohydrate moeties of the erythrocyte membrane during in vivo ageing.

Perturbational effects of inorganic cations on human erythrocyte membranes

The perturbational effects of monovalent and divalent cations on human erythrocyte membranes were analyzed by examining their influence on kinetic and structural characteristics of trinitrobenzenesulfonic acid (TNBS) incorporation into the amino groups of protein and phospholipid structural components. The stimulatory effects of monovalent cations on TNBS incorporation, which were size-independent and attributed to nonspecific membrane alterations resulting from ionic strength factors, contrasted with the more pronounced stimulatory properties of divalent cations which were markedly size-dependent. These stimulatory effects of cations on TNBS incorporation were associated with alterations not only in rate but also in activation energy in incorporation. Changes in activation energy produced by divalent cations paralleled their ability to perturb membrane protein components and probably reflected changes in probe permeation. The rate of TNBS incorporation exhibited a dependence on divalent cation ionic radius which paralleled ion-induced perturbations in the labelling of the membrane amino phospholipid phosphatidylethanolamine. Divalent cations differed both in the relative extent and in the characteristics of protein and phospholipid perturbation. Alkaline earth cations behaved as a rather homogeneous group while Ni++, Co++ and Mn++ constituted a second heterogeneous group. The influence of monovalent and divalent cations on the hemolytic behavior of intact erythrocytes paralleled their effects on TNBS incorporation into isolated membranes rather closely. It is suggested that TNBS incorporation may provide a valuable means of analyzing functionally relevant cation-induced alterations in biological membranes in general.