Rapid transport of proteins in the sonic motor system of the toadfish

A pure cholinergic, motor system of a marine fish has been utilized to study the kinetics and characteristics of proteins rapidly transported from the sonic motor nucleus to the musculature enveloping the swim bladder. Following microinjection of [3H]leucine, [3H]lysine, [35S]methionine, or [3H]fucose into the nucleus a wave of radioactivity was observed moving along the sonic motor nerves with an apparent rate of 96-120 mm/day. Analysis of the rapidly transported methionine-labeled protein using SDS gel electrophoresis revealed at least 9 major peaks of activity. Eight of these proteins were found to incorporate fucose, suggesting that most of the rapidly transported material consists of glycoproteins. These results are consistent with the previously suggested hypothesis relating the function of rapid transport to synaptic vesicles and the maintenance of pre-synaptic terminal membranes.