Two large glycosylated polypeptides found in myelinating oligodendrocytes but not in myelin

Previous work has shown that high molecular weight polypeptides sharing epitopes with myelin-associated glycoprotein are transiently expressed in developing human central nervous system. We describe here the isolation of two of these polypeptides (150 and 225 kDa), their biochemical characterization, and their immunochemical localization. They are both glycosylated and 15 kDa of the apparent molecular mass of both polypeptides is contributed by N-linked carbohydrate moiety(ies). Both have multimeric forms held together by disulfide bonds. Immunochemical and immunohistochemical studies failed to show these polypeptides in myelin. However, in developing human central nervous system, one or both of them are present in the perikaryal cytoplasm and processes of cells with morphology consistent with actively myelinating oligodendrocytes.