Synthesis, Migration and Turnover of Protein in Retinal Ganglion Cells

The synthesis, migration and turnover of proteins in retinal ganglion cells of the adult rabbit was studied after intraocular injections of [ 3 H]leucine. It was shown that the isotope was rapidly incorporated into proteins of the retina and some of the proteins were subsequently transported out into the axons of the retinal ganglion cells down to the terminals. This intra‐axonal transport of protein occurred at four different velocities; 150, 40, 6‐12 and 2 mm/day respectively. The two most rapidly migrating phases of axonal transport were predominantly associated with light particulate fractions and had a relatively rapid turnover in the nerve terminals in the lateral geniculate body. The third phase of axonal transport which had a rate of 6‐12 mm/day was possibly associated with the migration of mitochondria. The most slowly migrating proteins in the axon which moved at an average rate of 2 mm/day carried predominantly soluble proteins down to the nerve terminals. A minor part of this phase was metabolized locally in the axon with a half‐life of about 14 days. When this slowly migrating phase had reached the nerve terminals in the lateral geniculate body, it was degraded with a half‐life of 9‐6 days. The different phases of axonal transport were of different magnitudes. As measured from the maximal amount of radioactivity present in the nerve terminals the relative amounts of radioactivity of the four phases were: 1,1 ‐8,1 ‐5 and 8‐5.