Biochemical and morphological properties of bovine erythrocyte membrane glycoproteins

The major and minor sialoglycoproteins of the bovine erythrocyte have been solubilized and extensively purified. A comparison of composition revealed that the major glycoprotein had 77% carbohydrate and 23% peptide, and the minor one had 27% carbohydrate and 73% peptide. Molar ratios of sugars were related, however, the major glycoprotein had twice as much galactose and sialic acid as did the minor glycoprotein. Molecular weights, estimated from retardation coefficients of mobility in sodium dodecyl sulfate gel electrophoresis, were 55,000 for the major glycoprotein and 34,000 for the minor glycoprotein. The glycoproteins were studied by electron microscopy before and after delipidation and after ultracentrifugation. The major glycoprotein, prior to delipidation, formed large micelles. After delipidation, the major glycoprotein could not be visualized suggesting that it did not form aggregates in aqueous solution. The minor glycoprotein was visualized as rather uniform spherical aggregates (62 A average diameter) which tended to form short chains and small clumps. These characteristic aggregates were seen both before and after delipidation. After ultracentrifugation, fixation and sectioning both glycoproteins appeared to have formed microcrystalline arrays with average periodicity of 49 A.