Purification of the glial fibrillary acidic protein by anion-exchange chromatography

A procedure for the isolation of assembly-competent glial fibrillary acidic (GFA) protein from 2 m urea extracts of bovine spinal cord by anion-exchange chromatography is reported. The tissue was previously extracted with low-ionic-strength buffer. The procedure allowed the separation of nondegraded GFA protein from GFA protein comprising degraded species. As previously reported for neurofilament preparations obtained from porcine spinal cord (N. Geisler and K. Weber, J. Mol. Biol., 151, 565–571 (1981)), the procedure also allowed the simultaneous separation of the three neurofilament polypeptides (200,000; 150,000; and 70,000 daltons) contained in the 2 m urea extract. Brain filament proteins sequentially eluted at increasing salt concentration (25–200 mm NaCl) according to their isoelectric point. Proteins with higher pI eluted first. Tubulin eluted between the 200,000- and 150,000-dalton neurofilament polypeptides.