Adenylosuccinase activity of rat liver is depressed by prolonged
starvation,
cortisol administration,
high protein diets, and
alloxan diabetes. The loss of activity is not due to the accumulation of a dissociable inhibitor or loss of a cofactor.
Starvation produces no loss in activity for 1 day; thereafter the activities of the liver and spleen
enzyme decay with a half-life of about 0.9 day.
Starvation produces no change in the activity of the kidney, brain, and skeletal muscle
enzyme. Refeeding restores the activity of the liver
enzyme to the fed level, with only a slight overshoot. The recovery of
adenylosuccinase activity is equally rapid after refeeding a balanced diet, or
corn oil, or
glucose, and is not inhibited by injection of
glucagon, in contrast to malic
enzyme activity. Recovery is inhibited by
cycloheximide, indicating the involvement of
protein synthesis. Althouth
adenylosuccinase is depressed in liver of starving rat it is elevated in liver of starving chicken.
Starvation depresses malic
enzyme activity and elevates
alanine aminotransferase activity in both species. When rats are starved, the rate of de novo synthesis of
adenine mononucleotide decreases in spleen and liver but not in kidney, suggesting a regulatory role for
adenylosuccinase in
purine biosynthesis. The low activity of
adenylosuccinase in liver of severely starved rats is inconsistent with the proposal (Moss, K. M., and McGivan, J.D. (1975) Biochem. J. 150, 275-283) that the
purine nucleotide cycle plays a major role in
ammonia production for
urea synthesis, at least under these conditions.