Physicochemical properties of a human glycoprotein bearing blood group A activity

A human erythrocyte glycoprotein was isolated and purified from blood of group A+1 by a procedure involving chloroform-methanol extraction and affinity chromatography on Helix pomatia lectin-Sepharose 6MB, and some of its physicochemical properties were determined. The resulting preparation was homogeneous as indicated by polyacrylamide gel electrophoresis. The glycoprotein contained nearly 60% carbohydrate and 40% protein. It was water-soluble and inhibited the agglutination of A-erythrocytes. Its molecular weight was 41,900 (amino acid analysis) or 55,200 (light scattering), whereas electrophoresis revealed two bands of 43,000 and 76,000 Da. The ORD spectrum was consistent with 30% alpha-helix, 20% beta-sheet, and 50% random coil. Intrinsic viscosity was 14.61 ml.g-1, partial specific volume was roughly 0.66, isoelectric and isoionic points were 6.90 and 6.95, respectively. The glycoprotein differs from glycophorin and appears to be one of the minor glycoproteins of the human erythrocyte membrane.