Effect of hypothyroid status on adenosine 3',5'-monophosphate-dependent protein kinase of rat kidney

Changes in the properties of cyclic AMP-dependent protein kinase were studied in the kidney of hypothyroid rats. The activity of the crude extract was greater in hypothyroid rats than in normal ones. The ratio of type I isozyme to type II isozyme in hypothyroid rats was about twice that in the normal rats with enzymes from both the cortex and medulla. A higher affinity for the substrates was shown in the enzymes of the hypothyroid rat kidney. The effects of actinomycin D and of heat-stable protein kinase inhibitor on the enzyme activity were the same in both normal and hypothyroid rats. The changes in enzyme properties and isozyme distribution may well play an important role in the hypothyroid rat kidney.