Glial fibrillary acidic protein from normal and gliosed human brain. Demonstration of multiple related polypeptides

Abstract

An improved purification method for the glial fibrillary acidic protein from normal human brain is reported. Preparations of high purity were obtained by substituting DEAE and phosphocellulose chromatography with one step of hydroxylapatite chromatography. The glial fibrillary acidic protein from normal and gliosed brain was separated into 4 bands (components 1-4) ranging in molecular weight from 54 000 plus or minus 1000 to 40500 plus or minus 1000 by sodium dodecylsulfate gel electrophoresis at 7.5% and 12.5% acrylamide concentration. A better separation of the components was obtained on 12.5% acrylamide gels by increasing the time of electrophoresis to 15-17 h. In these conditions each component was split into a doublet. Preparations identical to those previously reported, i.e. 2-band preparations with an average molecular weight of 43 000, were obtained by incubating multiple sclerosis plaques at 24C for 48 h. These 2-band preparations co-migrated with the 2 lower molecular weight components (component 3, 45 000 plus or minus 1000; component 4, 40 500 plus or minus 1000) in 4-band preparations. The components cross-reacted with antisera against different preparations with an immunodiffusion pattern of complete identity and appeared to be chemically related. Most cyanogen bromide peptides were common to 2-band and 4-band preparations. A unique amino-terminal sequence of alanine-glycine-phenyl-alanine was found in all preparations, regardless of the source and of the number of components. The amino acid composition of 2-band and 4-band preparations was similar.