The Axon as a Heuristic Model for Studying Membrane Protein-Synthesizing Machinery

Abstract

It is perhaps no overstatement to say that little is known about the synthesizing machinery concerned with excitable-membrane protein synthesis. With the exception of the mitochondrion, there is a natural inclination to regard all protein synthesis in a cell, including that engaged with membrane renewal (i.e., membrane protein turnover) as being within the exclusive domain of the cytoplasmic, ribosomal machinery. However, one must not lose sight of the fact that the ribosomal system, as we presently conceive of it, synthesizes proteins for “export” (presumably at random) to other regions of the cell interior in order to satisfy local metabolic needs. Such a system, which I will refer to as “the centralized machinery,” would seem poorly adapted to fulfill the requirements for neuronal-membrane protein turnover. This may be true for plasma membranes of other specialized cell types as well. The thesis is based upon the fact that the neuronal plasma membrane is functionally differentiated on a regional basis. That is, its functional properties differ in contiguous regions, notwithstanding physical continuity of the membrane structure.

The studies reported here were supported by Public Health Service Research Grant No. NB 04036 from the National Institute of Neurological Diseases and Blindness.