Preparation of neurofilament protein from guinea pig peripheral nerve and spinal cord

A simple and rapid method for preparation of enriched neurofilament protein from mammalian peripheral nerve or spinal cord is described. Tissue extracts from guinea pig nerve or spinal cord are fractionated by ammonium sulfate fractionation, chromatography on Sepharofe 4B, and precipitation with ethanol. Molecular exclusion chromatography on Sepharose 4B, in which the neurofilament protein elutes quantitatively in the exclusion volume of the column, with little contamination by other proteins, is found to be a highly effective purification step. The protein is found to precipitate in ammonium sulfate fractions over a wide range of salt concentration, from 20 to 80% saturation. It is found to be quantitatively precipitated in 40% v/v ethanol-water. The preparative method described yields 0.25 mg of neurofilament protein per gram of nerve or spinal cord, with a purity of approximately 50%. The three principal neurofilament polypeptides, which have molecular weights by SDS-polyacrylamide gel electrophoresis os 200K, 145K, and 68K, are found to be present in the preparation in a molar ratio of 1:2:6. A variant form of neurofilament protein occurring in approximately 20% of Hartley strain guinea pigs is described, which has the polypeptide composition: 200K, 192K, 145K, 68K.