Protein synthesis activity in vitro in mouse tissues in relation to methionine-cysteine deficiency and age

The objective of this study was to determine whether ageing in the mouse is associated with changes in protein synthesis activity and response to dietary methionine-cysteine deficiency. Growing subadult mice (30-day-old) and adult mice (70-day-old) were compared. The amino acid restricted diet contained methionine and cysteine at a level of 10% that of the control diet. After a feeding period of 6 days protein synthesis activity was measured in liver, kidney and lung. In control liver, the level of protein synthesis activity was the same for the two age groups; in kidney and lung, activity was diminished in the adult group. After methionine-cysteine deficiency protein synthesis activity was unchanged in the subadult and diminished in the adult liver. In kidney, both age groups responded with an increase in activity. In lung, the subadult group remained unchanged and activity in the adult group was elevated. The amount of DNA/g wet weight of tissue was higher in the subadult than the adult group throughout. Methionine-cysteine deficiency resulted in an increase in DNA/g tissue wet weight, while the total amount of DNA in liver decreased, but was unchanged in kidney and lung. Total liver activity was decreased less in subadult than adult mice. Total kidney and lung activities were diminished in subadult but not adult mice. The results suggest that the specific protein synthesis activity of the ribosomes in the kidney and lung tends to decrease with age more readily than in liver, and that subadult liver displays less sensitivity towards methionine-cysteine deficiency than does adult liver.