Differential activation of type-I and type-II adenosine 3′:5′-cyclic monophosphate-dependent protein kinases in liver of glucagon-treated rats

Abstract

The protein-bound cyclic AMP and the activity of cytosolic protein kinases in the presence and absence of cyclic AMP were determined in rat liver up to 2h after injection of glucagon. On the basis of the different salt-sensitivities of the activated cyclic AMP-dependent proteinkinases I and II, an activation of protein kinase II restricted to the high cyclic AMP concentrations present in the first 30 min after hormone injection was found. Essentially the same result was obtained by chromatographic analysis on DEAE-cellulose of liver cytosol from untreated rats and from rats killed at 2 and 60 min after glucagon injection. Protein kinase II activation was only detected at 2 min after injection. In contrast, the cyclic AMP-dependent protein kinase I was found to be nearly totally activated at 2 min and to be still almost as active at 60 min after the hormone stimulus, whereas the amount of bound cyclic AMP and the activation of total cytosolic protein kinases had fallen to two-thirds of their maximal values during this time period. A third cyclic AMP-independent protein kinase, which co-chromatographed with protein kinase type II, could be clearly distinguished from the two cyclic AMP-dependent kinases by use of the heat-stable inhibitor from bovine muscle, which totally inhibited the cyclic AMP-dependent enzymes, but stimulated the cyclic AMP-independent protein kinase.