Astroglial and axonal proteins in isolated brain filaments. I. Isolation of the glial fibrillary acidic protein and of an immunologically active cyanogen bromide peptide from brain filament preparations of bovine white matter.

The glial fibrillary acidic protein and an immunologically active cyanogen bromide peptide were purified by immunoaffinity chromatography from 8 M urea extracts of brain filament preparations isolated from bovine white matter according to Norton's procedure. The protein accounted for approximately 30% of the total protein in this preparation and for the largest fraction in the 50 000 molecular weight range. The fraction not absorbed to the immuno-Sepharose column reacted with neurofilament antisera by double immunodiffusion. On sodium dodecyl sulfate gel electrophoresis the main bands in the non-adsorbed fraction were at 74 000 daltons and above 100 000. Several bands were seen in the 50 000 molecular weight range. It is concluded that glio- and neurofilaments co-purify together in Norton's procedure and that neurofilaments are probably heterogeneous in polypeptide composition.