Effect of a prolonged protein-free diet on cell size, protein synthesis and degradation of rat liver.

Rats were fed a protein-free diet. After 9 weeks the animals' weight decreased to about 50% of the original. The liver weight was also decreased to about half, and most interestingly the average size of the liver cells was reduced about 50%. Liver protein synthesis was approximately 75% of controls tested in an "in vitro" system. Polysomes were found disaggregated in livers of rats on protein-free diet. This was not due to a reduced content or translatability of mRNA. eIF-2 partially purified from livers of rats on protein-free diet had the same activity as that from controls. The decrease of ATP, ADP and AMP in livers of rats on protein-free diet (19%, 42% and 58% respectively) may be responsible for the decreased rate of initiation of protein synthesis. Proteolysis in liver cytosol from rats on protein-free diet was 50% higher than in controls mostly due to lysosomal proteolysis.