A LOW MOLECULAR W eight GLYCOPROTEIN ASSOCIATED WITH ISOLATED MYELIN: DISTINCTION FROM MYELIN PROTEOLIPID PROTEIN

Abstract— A low molecular weight glycoprotein has been demonstrated in myelin isolated from immature rat brains. Both short term and long term fucose incorporation studies have identified this protein in the proteolipid protein region of a sodium dodecyl sulfate, polyacrylamide gel. A 1.7-2.1 fold increase in radioactive fucose in this glycoprotein relative to the major myelin glycoprotein was seen after long term fucose incorporation (21 days) compared to short term incorporation (18–22 h). The demonstration that this fucose-labelled protein is distinguishable from that of proteolipid protein was achieved by a variety of independent techniques. One technique involved a comparison of ether-ethanol extracted, freshly isolated, myelin with myelin extracted with chloroform-methanol. Treatment of isolated myelin with chloroform-methanol results in the solubilization of the proteolopid protein and its subsequent absence on gel electrophoresis while, in contrast, an enhancement of fucose label was observed in the same region of the polyacrylamide gel. Another procedure involved the electrophoretic separation of the radioactive fucose peak from that of proteolipid protein by employing a continuous, phosphate buffered, gel system. Finally carbohydrate analysis by gas-liquid chromatography of a partially purified proteolipid protein fraction did not reveal significant amounts of carbohydrates which are characteristic of glycoproteins. The identification of this minor glycoprotein comigrating with proteolipid protein indicates, therefore, a greater complexity associated with the purified myelin membrane than has been previously demonstrated.