FRACTIONATION OF GLYCOPROTEINS ASSOCIATED TO ADULT RAT BRAIN MYELIN FRACTIONS

Abstract

Abstract— The chloroform‐methanol insoluble residue of adult rat brain myelin fractions (My‐CMI) contains only 20% of protein but all myelin‐associated glycoproteins (Z anetta et al ., 1977a). After solubilization in sodium dodecyl sulphate, these glycoproteins were separated by sequential affinity chromatography on 4 immobilized lectins. Ten fractions (9 of which contained only glycoproteins) were obtained. Glycoproteins added up to at least 25% of My‐CMI proteins. Many minor glycoproteins were detected in the different fractions. However most of them appeared not to be intrinsic to myelin. On the contrary a major glycoprotein electrophoretic band, component A, appeared to be intrinsic to myelin although its presence also on oligodendrocyte plasma membrane cannot be excluded. Component A was tentatively identified with the‘major myelin associated glycoprotein’described by QUARLES (1972, 1973 a, b ). It accounted for less than 0.4% of proteins and 8% of glycoproteins of myelin fractions and consisted of at least two‘glycopolypeptides’which, both, bind to concanavalin A and to the Ulex europeus lectin. The other major glycoprotein, component B, did not bind to any of the lectins used and, thus, must have N ‐acetyl neuraminic acid as only terminal sugar. The separation of myelin‐associated glycoproteins according to their affinity for lectins allowed a tentative identification of the lectin binding sites of myelin sheath.