The Nature of the Cell Surface Receptor Site for Lens culinaris Phytohemagglutinin

Abstract

Abstract Human erythrocytes contain about 500,000 receptors for a phytohemagglutinin (PHA) derived from the common lentil. When erythrocytes are treated with trypsin, there is a 50% decrease in the number of lentil PHA molecules bound to the cells. The glycoprotein material released from the cells by trypsin as well as a highly purified glycopeptide derived from it, previously shown to be a receptor for kidney bean PHA, have potent lentil PHA haptene inhibitory activity. In addition, a number of glycopeptides derived from serum proteins possess haptene inhibitory activity. The most potent of these is the glycopeptide of γG-immunoglobulin. Serial enzymatic degradation of active glycopeptides has revealed that the specificity for binding to lentil PHA resides in the oligosaccharide portion of the glycopeptide molecules with the determinant sugars being the N-acetylglucosamine residues of the outer branches and the mannose residues of the core. However, the simplest sugars, N-acetylglucosamine and mannose, are extremely poor haptene inhibitors compared to the intact glycopeptides. Lentil PHA and kidney bean PHA may bind to different portions of the same oligosaccharide on the human erythrocyte surface.