Abstract— Several amino acids, particularly [3H]proline and [3H]asparagine specifically and efficiently labelled rapidly transported proteins in the goldfish optic nerve and tectum after intraocular injection. Studies with these amino acids showed that the rapidly transported proteins moved as a discrete band at a rate which was temperature‐dependent, and was equal to 70‐100 mm per day at 20°C. Transported protein in the optic tectum was 80 per cent particulate and was found in synaptosomal, mitochondrial, and myelin fractions, but not in purified nuclei or ribosomes.
SUMMARY "-Proline, "H-asparagine and Na2W04 have been found to be highly specific markers for axonal transport in the goldfish visual system. The amino acids label both rapidly and slowly transported proteins while the 35S is recovered mainly with the rapidly transported materials, including protein-bound mucopolysaccharides. These precursors have been used t o study the rate of transport, the subcellular distribution and the rate of turnover of transported proteins in the nerve terminals.
Proteins undergoing rapid axonal transport in the garfish olfactory nerve were examined by sodium dodecyl sulphate gel electrophoresis. The distribution of polypeptides and the extent of their labeling by transported molecules was determined in several nerve subfractions including: total particulate, total membrane, mitochondrial and two membrane subfractions rich in axolemma. The polypeptide composition of the various fractions was found to be relatively similar, with each showing a major protein with an estimated MW of 58,000. Specific differences in the concentrations of certain proteins were noted between fractions, including differences between the lower and higher density axolemma rich subfractions. Axonally transported radioactivity was predominantly localized among high molecular weight proteins, with all fractions, except mitochondrial pellet, displaying a major peak of radioactivity centered at 126.000-MW. Several major proteins including the 58.000-MW band were labeled by rapid transport to a much smaller extent. Certain labeled peaks were found to be concentrated in individual fractions. particularly a polypeptide (MW 35.000) more predominantly found in the lower density axolemma rich fraction.Systemic labeling of the nerve is found to give a general distribution of radioactivity on gels, which is clearly different from the pattern obtained after axonal transport labeling.
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