SUBCELLULAR AND POLYPEPTIDE DISTRIBUTIONS OF SLOWLY TRANSPORTED PROTEINS IN THE GARFISH OLFACTORY NERVE

In the garfish [Lepisosteus osseus] olfactory nerve proteins labeled with [3H]leucine are transported by slow axonal flow as a well-defined crest of radioactivity. At 21.degree. C slow flow moves along the axon with a velocity of 0.92 .+-. 0.02 mm/day. Four subcellular fractions (soluble, mitochondrial and 2 membranous) and their polypeptide composition were analyzed in areas of the nerve containing the slow moving crest, the material remaining in the nerve behind the crest and the labeling present in front of the slow crest. Analyses were done 70 and 110 days after isotope deposition. The crest of slow moving radioactivity is characterized by a close parallel between labeling and protein concentration in the subcellular fractions and among the polypeptides constituting these fractions. The radioactivity is mainly associated with MW of 14,000, 30-45,000 58,000 and 68,000. The composition of the moving crest remains essentially constant during the 40 day period investigated. Most of the slow-moving molecules remain in the axon behind the moving crest. This deposited material appears to be redistributed and/or to be turning over more rapidly than the molecules still moving in the crest. A large amount of radioactivity was recovered in front of the moving crest. This might be produced by molecules deposited by fast transport and by material released from the cell body at rates intermediate between the fast and slow phases of transport. The subcellular and polypeptide compositions of this area of the nerve remain constant and are intermediate between the compositions of fast and slow flow. The slowly transported labeled polypeptides in the mitochondrial fraction are of low MW, and were similar in the various areas of the nerve and at the 2 time points studied, and were even similar to the polypeptide distribution determined for fast transport.