Isolation of neurofilament proteins and of immunologically active neurofilament degradation products from extracts of brain, spinal cord and sciatic nerve.

This paper reports the isolation by immunoaffinity chromatography of neurofilament proteins from 1 mM sodium phosphate buffer extracts of brain, spinal cord and sciatic nerve in four mammalian species: human, bovine, rabbit and rat. Antisera were prepared against degraded chicken neurofilament proteins as previously described. The main polypeptides isolated in the fraction tightly attached to the column and eluted at pH 2.9 were at 72 and at approx. 150 kdaltons. In rat and rabbit the approx. 150-kdalton neurofilament polypeptide was apparently smaller compared with bovine and human as indicated by comigration experiments on sodium dodecyl sulfate polyacrylamide gel electrophoresis. The 200-kdalton neurofilament polypeptide was less tightly attached to the immunoaffinity column and was preferentially eluted at pH 6.0 in 5 M urea. Variable amounts of degraded products were also present in most purified preparations. Degradation was markedly increased by the omission of EDTA in the extraction and column buffers. In the rat, degraded proteins isolated on the immunoaffinity column in the absence of EDTA were at 68 and 55 kdaltons.