Dynamic condition of proteins in the visual cells of rats and mice as shown by radioautography with labeled amino acids

The behavior of proteins in retinal rods was examined by injecting various labeled amino acids (methionine‐S35 and ‐H3, tyrosine‐, leucine‐, and arginine‐H3) into rats and mice, which were sacrificed at different time intervals between 10 minutes and 30 days. The retina of these animals was then radioautographed. Within minutes after injection of any one of the listed amino acids, a radioautographic reaction appears over the inner segment of the rods. This region of the cell is therefore a site of protein synthesis. Since this synthesis may be seen at any time of the day, it must be a continuous phenomenon. At 24 hours after injection, the radioautographic reaction appears over the junction of the inner and outer segments, and at 1.5–4 days, over the outer segment. Hence, the recently synthesized protein progressively migrates from the inner, toward and into the outer segment. Analysis of the decay of the specific activity in the inner segment reveals that two categories of proteins are synthesized there. One is a slowly turning over protein, presumably catabolized in situ and referred to as “sedentary.” The other is a fast turning over protein, which migrates into the outer segment and is referred to as “exportable”. The exportable protein may be opsin.