Activation of microsomal cAMP-dependent protein kinase isoenzyme I by ACTH1-24 in bovine adrenal cells.

In microsomes of bovine fasciculata reticularis cells incubated with or without 10(-8) M ACTH during 20 min, we measured covalent and non covalent cAMP binding under exchange or non-exchange conditions and cAMP-kinase activity. ACTH induced a decrease in cAMP-kinase activity and in the number of free cAMP binding sites. These results indicate an activation by ACTH of a part of microsomal cAMP-dependent protein kinase. Photoaffinity labeling of microsomal protein with 8-azido-cAMP revealed the presence of both cAMP-kinase isoenzyme I and II in this cellular fraction. Using this method, it was demonstrated that ACTH1-24 caused a preferential and nearly complete activation of microsomal protein kinase I.