Stable polymers of the axonal cytoskeleton: the axoplasmic ghost.

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Abstract
The monomer-polymer equilibria which form the cytoskeletal polymers in squid axoplasm were studied by extracting protein at low concentrations of monomer. The solution conditions inside the axon were matched as closely as possibly by the extraction buffer (buffer P) to preserve the types of protein associations that occur in axoplasm. Upon extraction in buffer P, all of the neurofilament proteins in axoplasm remain polymerized as part of the stable of neurofilament network. Most of the polymerized tubulin and actin in axoplasm is soluble although a fraction of these proteins also exists as a stable polymer. The axoplasmic cytoskeleton contains stable polymers and soluble polymers. Stable polymers, such as neurofilaments, conserve cytoskeletal organization because they tend to remain polymerized; soluble polymers increase the plasticity of the cytoskeleton because they permit rapid and reversible changes in cytoskeletal organization.