Modification of sialyl residues of sialoglycoprotein(s) of the human erythrocyte surface.

Modification of erythrocyte membrane sialoglycoprotein(s) in isolated form, or when in membrane, is described using sequential sodium periodate oxidation and tritiated sodium borohydride reduction, essentially as suggested by Van Lenten and Ashwell ((19’71) J. Bio2. Chem. 246, 1889). Conditions of modification were investigated; under the optimal but nondestructive conditions selected, the modification appears specific for sialyl residues and leads to incorporation of tritium into the modified product, 5-acetamido3,5-dideoxy-L-arabino-2-heptulosonic acid, identified by its susceptibility to neuraminidase and mild acid hydrolysis, and by its identity with the authentic compound in chromatographic behavior, several calorimetric assays, and extent of tritium incorporation. The selectivity of the modification for the sialoglycoprotein(s) is further demonstrated by carrying out the modification on solubilized membrane proteins; only the sialoglycoprotein(s) incorporates the label. In the modification of the intact membranes some lipid components also become radioactive. The modification of intact erythrocytes, the membranes, or the isolated sialoglycoprotein(s) results in loss of the M blood group activity, but the A and B blood group activities and the phytohemagglutinin binding sites are not affected. The modification offers a handle for isolation of membrane sialoglycoprotein(s) and study of their disposition, and possibly, for evaluation of the physiological role of the terminal polyhydroxy side chains of their sialyl residues.