Isolation and initial characterization of glial fibrillary acidic protein from chicken, turtle, frog and fish central...

The purification procedure for mammalian glial fibrillary acidic protein allowed the isolation of related proteins from the brain and spinal cord of the chicken, turtle, frog and fish. With the exception of the turtle, the proteins so isolated were homogeneous and migrated as a single band on sodium dodecyl sulfate-acrylamide gel electrophoresis, displaying the same mobility as bovine glial fibrillary acidic protein, 54 000 mol. wt. In the turtle an additional slower migrating band was constantly present, together with the main species. Mammalian and submammalian proteins were similar in amino acid composition and appeared to be susceptible to the same type of in situ proteolysis, with degradation of the major species into multiple polypeptides ranging down to 40 500 mol. wt. Unless degraded, the proteins isolated from submammalian vertebrates were excluded from sodium dodecyl sulfate-acrylamide gels if a reducing agent was not added to the electrophoretic sample, thus suggesting the existance of disulfide bridges between polypeptide chains, as demonstrated for the mammalian protein. The purified submammalian antigens cross-reacted with antisera to human glial fibrillary acidic protein with formation of spurs not only at the junction between mammalian and submammalian precipitation lines, but also between submammalian lines. The antisera produced against chicken antigen did not react with the human antigen and the antichicken sera could not be absorbed with human antigen. An immunologically active cyanogen bromide peptide in the myoglobin range (17 200 mol. wt.) characteristic of the mammalian protein, degraded and nondegraded, was not present in the digest of the submammalian proteins.