Relative susceptibilities to neuraminidase of the glycoproteins of the human erythrorcyte

Release of sialic acid from the glycoproteins of the normal human erythrocyte surface by neuraminidase was investigated. The glycoproteins of the membrane were separated by electrophoresis in sodium dodecylsulfate polyacrylamide gels. Sialic acid was determined in the sliced gel by a modification of the 2-thiobarbituric acid method, revealing three sialic acid-containing glycoproteins. Treatment of intact erythrocytes with neuraminidase to remove varying amounts of sialic acid indicates that all the glycoproteins are essentially equally accessible to the neuraminidase when 20%–60% of the sialic acid is removed. Similar but not quite identical results were obtained with isolated erythrocyte membranes.Treatment of intact cells with the lectins concanavalin A or phytohemagglutinin-P resulted in shielding of about 25% and 50%, respectively, of the sialic acid from neuraminidase. Concanavalin A blocked sialic acid release over long time periods and with high concentrations of neuraminidase. In contrast, the sialic acid shielding by phytohemagglutinin-P can be overcome by high concentrations of neuraminidase. Both lectins were found to shield the various glycoproteins selectively, with different patterns of shielding. Wheat germ agglutinin exhibited no detectable effect on the susceptibility of the erythrocyte sialic acid to neuraminidase.