Influence of dietary restriction on accumulation of heat-labile enzyme molecules in the liver and brain of mice.

The influence of dietary restriction on alterations of two aminoacyl-tRNA synthetases was investigated in mouse tissues. Mice were fed a restricted diet (first 80% and then 60% of the ad libitum intake) from 23.5 months of age for 70 days. Before dietary restriction, about 35 and 25% of these enzymes in the brain and liver, respectively, were heat-labile. Dietary restriction resulted in a decrease in the percentage of heat-labile enzyme in both tissues: After 40 and 70 days of dietary restriction the percentage of heat-labile enzyme decreased to about 20 and 10%, respectively, in the brain and to undetectable or very low levels in the liver. These results suggest an interesting possibility that prolongation of the life span by dietary restriction is due to reduction in the level of altered enzyme molecules whose accumulation may be detrimental to cellular functions.