Slow axonal protein transport and axoplasmic organization

A recently formulated structural theory of axonal transport suggests that each group of transported material is a distinct class of functionally related structures and that the proteins making up those structures, with few exceptions, are found in only one rate component, thus maintaining a close noncovalent association during transport. If such a relationship exists, one would postulate that the labelled proteins at the leading edge and trailing edge of a rate component following a pulse of radioactive amino acid would be present in similar proportions. After retinal ganglion cell proteins were labelled by intraocular injection of radioactive amino acid in the guinea pig eye, the optic nerve and tract were analyzed at several post-injection intervals. The data thus derived support the existence of a close relationship among the "soluble" proteins of slow component b and are consistent with the structural concept of axonal transport. If diffusion were the mechanism of transport, the larger proteins would be expected to move slower than the smaller proteins. Such insights into the process of axonal transport should help to identify the variables critical to survival of neurons following acute trauma and degenerative diseases.