Effect of dietary protein content on the activity of rat liver asparagine synthetase

The activity of rat liver asparagine synthetase [EC 6.3.1.1]increased when animals maintained on 25% protein diet were placed on 15% or 6% protein diet. The enzyme activity level rose within one day, reached a maximum in 7 or 10 days after switching the diet and thereafter dropped gradually. During the purification of the enzyme from rats on 25% or 6% protein diet, the yield and increase of the specific activity were similar in the two groups. Combination of the liver extracts from two such groups demonstrated that the amount of endogeneous inhibitors of the enzyme did not change on replacing the diet. The elevation of the enzyme activity in rats fed 6% casein diet was suppressed by an injection of cycloheximide or actinomycin D. It is suggested that the change in the enzyme activity was due to alteration of the amount of the enzyme.