Age-associated changes in poly(adenylate) polymerase of rat liver and brain

The activity of poly(adenylate) polymerase was measured in nuclear lysates of rat brain and liver of animals ranging from 25 to 300 days. The activity was 26 nmoles AMP incorporated per h per mg of protein in liver and 8 moles per h mg in brain for 25-day-old rats, and declined to 1.0 and 3.3 for liver and brain, respectively, in 300-day-old rats. At all ages the liver showed a linear time course and had a Km for ATP of 0.5 mM. The brain enzyme gave a non-linear time course at all ages with an ATP optimum of 0.2 mM. Mixing enzyme preparations from young and old animals produced additive results. Mixing brain and liver enzyme produced greater than additive results. No substantial increase in activity was observed when enzyme was prepared from old or young partially hepatectomized rats as compared to sham-operated controls.