Differences in the composition of the polypeptides deposited in the axon and the nerve terminals by fast axonal transport in the garfish olfactory nerve.

Proteins transported by the fast wave of axonal transport have been shown to be deposited both in the axon and in the nerve terminals. Differences in the nature of the molecules deposited in these two areas were studied in the garfish olfactory system. In order to avoid analysis of transported molecules in two different types of tissue like the olfactory nerve and the olfactory bulb, the study was conducted (1) by comparing the composition of the moving crest of radioactivity at two different points along the nerve: when the crest enters the axon and when it reaches a distance of approximatively 5 cm from the nerve endings, (2) by determining the composition of the molecules remaining in the axon behind the moving crest. Three subcellular fractions (two membranous fractions and a mitochondrial pellet) were investigated. In both membranous fractions the majority of the polypeptides deposited in the axon ranged from 50 to 150,000 daltons. No outstanding peak of radioactivity was found in either fraction. Radioactivity was relatively evenly distributed among the various polypeptides. In the lightest membranous fraction, however, a peak (mol. wt., 54-58,000) was more particularly deposited in the axon. The opposite situation was found for the molecules moving toward the synapses: transported radioactivity was concentrated in a few distinct polypeptides, while the others were significantly less labeled. Three peaks were found in the lightest membranous fraction (mol. wt., 35,000, 54-58,000 and 126,000). Only two peaks were determined in the heaviest fraction (mol. wt., 58,000 and 126,000). The 126,000 mol. wt. peak increases with distance in both membranous fractions from 9 to 12% of the total radioactivity and moves mainly toward the synapses. The 35,000 mol. wt. polypeptide presented some interesting properties: it was found in larger quantities in the lightest membranous fraction; labeling was very poor in the heaviest membranous fraction, and finally this polypeptide appeared to be largely transported to the synapses. Results concerning the polypeptide composition and the composition of the transported molecules indicated that the lightest fraction may contain more synaptosomal material. From this study it appears that most transported polypeptides are distributed in both the axon and the nerve terminals, but that the percentage delivered to each area varies. A few distinct polypeptides on the contrary are more selectively transported to the synapses and are even differently localized in subcellular fractions.