Isolation and Biochemical Characterization of a Neural Proteoglycan Expressing the L5 Carbohydrate Epitope

Abstract: The monoclonal L5 antibody reacts with an N‐glycosidically linked carbohydrate structure which is present on the neural cell adhesion molecule L1, neural chondroitin sulfate proteoglycans, and other not yet identified glycosylated proteins. Using this antibody, we isolated and characterized proteoglycans from adult mouse brain and cultured astrocytes biosynthetically labeled with Na₂³⁵SO₄ and a ³H‐amino acid mixture. Our data suggest that the L5 proteoglycans of both sources are identical in their biochemical properties. The apparent molecular mass of the L5 proteoglycan is approximately 500 kDa. Digestion of the iodinated L5 proteoglycan from mouse brain and of the [³⁵S]methionine‐labeled L5 proteoglycan from cultured astrocytes with proteinase‐free chondroitinases ABC and AC revealed three major core proteins with apparent molecular masses of approximately 380, 360, and 260 kDa. These represent molecularly distinct protein cores.