Association of human erythrocyte membrane glycoproteins with blood-group Cad specificity

Publisher Website
Google Scholar
Abstract
Sodium dodecyl sulfate/polyacrylamide-gel electrophoresis of erythrocyte membranes from a blood-group-B individual with the rare Cad phenotype indicates a lower-than-normal mobility of the main sialoglycoproteins, suggesting an increase in apparent molecular mass of 3kDa [kilodaltons] and 2 kDa, respectively for glycoprotein a (synonym glycophorin A) and glycoprotein .delta. (synonym glycophorin B). Since the chief structural determinant of Cad specificity is N-acetylgalactosamine, the membrane receptors were isolated by affinity binding on immobilized Dolichos biflorus (horse gram) lectin. The predominant species eluted from the gel was the abnormal glycoprotein a, whereas in control experiments no material could be recovered from the adsorbant incubated with group-B Cad-negative erythrocyte membranes. After partition of the membranes with organic solvents, the blood-group-Cad activity was found in aqueous phases containing the sialoglycoproteins, but not in the organic phases containing simple or complex glycolipids, which retained the blood-group-B activity. The carbohydrate composition of highly purified lipid-free glycoprotein a molecules prepared from Cad and control erythrocytes was determined. The molar ratio of N-acetylneuraminic acid to N-acetylgalactosamine was equal to 2:1 in the case of controls and equal to 1:1 in the case of Cad erythrocytes. Cad specificity is apparently defined by N-acetylgalactosamine residues carried by the alkali-labile oligosaccharide chains attached to the erythrocyte membrane sialoglycoproteins.