Isolation of intermediate filaments from rat astrocytes in culture.

Intermediate filaments from rat astrocytes in culture were isolated by subcellular fractionation. The fractionation was monitored by electron microscopy and by quantitative immunoelectrophoresis using rabbit antibody directed against human glial fibrillary acidic protein (GFA). Morphologically intermediate filaments appeared helical with a mean diameter of 10 nm. Isolated filaments were disassembled at highly alkaline pH. After lowering of pH to slightly acidic values reassembled filaments, approximately 17 nm in diameter, were observed. As revealed by sodium dodecyl sulfate polyacrylamide gel electrophoresis the filament preparation was composed predominantly of a 51,000 molecular weight protein, corresponding to GFA. At high loads additional proteins of molecular weights 43,000 and 58,000 were detected. These latter proteins may represent residual actin and vimentin, respectively.