Protein loss from axonal transport occurs without diminution of vesicle traffic

Protein loss from the rapid anterograde axonal transport system of amphibian sensory nerve fibers was compared with the numbers and sizes of anterogradely transported vesicles in the axons. Protein was found to be lost at a rate of approximately 2% per millimeter of nerve traversed. However, no changes were observed in either the numbers or sizes of vesicles in the nerve at two locations separated by 60-75 mm. The results show that protein loss is not explained as a loss of vesicles from the transport system nor by a reduction in vesicle size.