Components of fast and slow axonal transport in the goldfish optic nerve

The composition of the fast and slow components of axonal transport in the goldfish optic nerve was investigated, using specific radioactive precursors injected into the eye. Tritiated glucosamine and fucose label macromolecules, presumably glycoproteins, which are rapidly transported from the eye to the optic tectum. Material labeled with these precursors is not evident in the slowly transported component. Glucosamine and fucose incorporation are blocked when a protein synthesis inhibitor, acetoxycycloheximide, is injected into the eye concurrently with the precursors. As well as labeling macromolecules, ³H-glucosamine and ³H-N-acetylmannosamine ( a precursor of sialic acids) also label rapidly-transported chloroform-methanol-extractable material which may contain transported glycolipids. Two procedures were used to show that the slow component of axonal transport contains tubulin, a protein characteristic of the microtubules:

• (a) Tracer doses of tritiated colchicine injected into the eye label a wave of radioactivity which moves 0.5 mm/day, the rate of slow axonal transport in the goldfish optic nerve. We believe this wave represents the movement of colchicine which is bound to colchicine-binding protein moving in the slow component of axonal transport.
• (b) Tritiated proline labels a slowly transported protein which is precipitated by vinblastine and has a mobility on polyacrylamide gels comparable to authentic tubulin. These results indicate that the fast and slow components of axonal transport each provide specific chemical substances to the nerve endings.