Metabolic studies in vitro of the CNS cytoskeletal proteins: Synthesis and degradation
General aspects of metabolic features of the most prominent CNS intermediate filament proteins, the 200,000 (200K), 150,000 (150K), and 70,000 (70K) dalton proteins of the neuron, and the glial fibrillary acidic protein (GFAP) have been explored using the incubated spinal cord slice from the rat. Measurement of shortterm uptake of3H-labeled amino acids into the individual proteins separated on polyacrylamide gels revealed that of the three neurofilament proteins, 200K was most metabolically active, 150K was less active, and 70K contained very little incorporated radioactivity. Glial fibrillary acidic protein based on Coomassie blue stain affinity showed less metabolic activity than any of the neurofilament proteins. Those relationships were constant at all ages, but the metabolic activity of all CNS intermediate filaments decreased with age. When Ca2+ was present in the medium of the incubated slices, the intermediate filaments were rapidly destroyed, but GFAP was more resistant to degradation than the neurofilament proteins. GFAP and probably the neurofilament proteins also were relatively resistant to Ca2+-activated degradative mechanisms in spinal cords of rats at younger ages (15 day) than in those of older animals (10–18 months). It is likely that the Ca2+ activated protease is less active in developing animals in which the nerve tracts are still elongating, than in adults. These results suggest that GFAP is less active metabolically and more resistant to degradation than the neurofilament proteins at all stages of maturation, but that metabolic activity of all CNS intermediate filaments decreases with age while the susceptibility to degradation increases.
KeywordsSpinal Cord Metabolic Activity Glial Fibrillary Acidic Protein Coomassie Intermediate Filament
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- 1.Norton, W. T., andGoldman, J. E. 1980. Neurofilaments. Pages 301–329,in Bradshaw, R. A., andSchneider, D. M. (eds.), Proteins of the Nervous System, Raven Press, New York.Google Scholar
- 2.Chiu, F.-C., Goldman, J. E., andNorton, W. T. 1983. Biochemistry of neurofilaments. Pages 27–56,in Marotta, C. A. (ed.) Neurofilaments, University of Minnesota Press, Minneapolis.Google Scholar
- 3.Eng, L. F. 1980. The glial fibrillary acidic protein. Pages 85–117,in Bradshaw, R. A., andSchneider, D. M. (eds.), Proteins of the Nervous System, Raven Press, New York.Google Scholar
- 6.Laemmli, U. K. 1970. Cleavage of structural proteins during the assembly of the head of bacteriophage T4. Nature (Lond.) 227:680–685.Google Scholar
- 11.Eng, L. F., andRubinstein, L. J. 1978. Contribution of immunohisto-chemistry to diagnostic problems of human cerebral tumors. J. Histochem. Cytochem. 25:513–522.Google Scholar
- 12.Sternberger, L. A. 1979. Immunocytochemistry. John Wiley and Sons, New York.Google Scholar
- 14.Ellisman, M. H., andPorter, K. R. 1983. Introduction to the cytoskeleton. Pages 3–26,in Marotta, C. A. (ed.), Neurofilaments, University of Minnesota Press, Minneapolis.Google Scholar
- 17.Lasek, R. J., andBlack, M. M. 1977. How do axons stop growing? Some clues from the metabolism of the proteins in the slow component of axonal transport. Pages 161–169,in Roberts, S., Lajtha, A., andGispen, W. H. (eds.), Mechanisms, Regulation, and Special Functions of Protein Synthesis of the Brain, Elsevier, North Holland, Amsterdam.Google Scholar
- 18.Willard, M. 1983. Neurofilaments and axonal transport. Pages 86–116,in Marotta, C. A. (ed.), Neurofilaments, University of Minnesota Press, Minneapolis.Google Scholar
- 21.Nixon, R. A. 1983. Proteolysis of neurofilaments. Pages 117–154,in Marotta, C. A. (ed.), Neurofilaments, University of Minnesota Press, Minneapolis.Google Scholar