Subcellular fractionation of intra-axonally transport polypeptides in the rabbit visual system.

We analyzed the subcellular distributions of proteins that are transported down the axons of rabbit retinal ganglion cells and compared these distributions to those of enzyme markers for endoplasmic reticulum, plasma membrane, and mitochondria. The proteins of each of five previously identified transport groups were uniquely distributed through the subcellular fractions, suggesting that each transport group is associated with different subcellular organelles. In particular, all of the observed group I polypeptides (the most rapidly moving, group, maximum velocity greater than 240 mm/day) were associated with material of hydrodynamic properties similar to those of the plasma membrane. The proteins of group II (maximum velocity = 34--68 mm/day) were heterogenous in their subcellular distributions but included mitochondrial proteins. Groups III and IV (maximum velocity = 4--8 and 2--4 mm/day, respectively) included materials that may be involved in motile processes; group V (maximum velocity = 0.7--1.1 mm/day) contained material of very high density which may be associated with neurofilaments.