Dissociation of monomer ribosomes into subunits by liver and hepatoma DF extracts and its relation with age

The changes with age of 80S monomer ribosome dissociation into subunits by factors extracted from the ribosomal 0.5 M KCl wash and from the high-speed supernatant (S-100 fraction) of rat liver and, for comparison, of the Yoshida ascites hepatoma cells have been examined and compared. Marked, statistically significant, reductions of dissociating activity appear to occur in aging 25-month-old rats. Higher, statistically significant, dissociating activities are, on the contrary, shown by middle-aged 13-month-old rats. Young adult 6-month-old rats show some dissociating activity when the DF extracted from the S-100 fraction is tested. The highest, statistically significant, dissociating activity is shown by factors from Yoshida ascites hepatoma cells, primarily when extracted from the S-100 fraction. Since dissociation of ribosomes precedes initiation of protein synthesis it appears possible that reductions in the initiation process occur during aging. This might account for the reduced rate of protein synthesis in these conditions.