[^{3 5}S]Sulfate incorporation into myelin glycoproteins I. Central nervous system

The in vivo incorporation of [^{3 5}S]sulfate and [³H]fucose into rat brain myelin was investigated. Most of the ^{3 5}S in the myelin was in sulfatide, but about 4% was associated with the residual proteins after chloroform/methanol extraction. Polyacrylamide gel electrophoresis of these proteins indicated that the major ^{3 5}S-labeled component corresponded to the major fucose-labeled glycoprotein. The labeling of this predominant glycoprotein with sulfate was more selective than with fucose, since there was relatively little incorporation of sulfate into some of the minor fucose-labeled glycoproteins. There was little or no ^{3 5}S associated with proteolipid or basic protein on polyacrylamide gels. The fucose-labeled glycoproteins were converted to glycopeptides by pronase digestion and separated into two major classes by gel filtration on Sephadex-G50. Only the higher molecular weight class contained significant amounts of ^{3 5}S. The association of ^{3 5}S with the glycopeptides was not due to binding of sulfatide or free inorganic sulfate. The results indicate that the predominant myelin-associated glycoprotein in rat brain is sulfated.