Activation of microsomal c AMP-dependent protein kinase isoenzyme I by ACTH 1–24 in bovine adrenal cells

Abstract

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 ofmicrosomal 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 ACTH 1–24 caused a preferential and nearly complete activation ofmicrosomal protein kinase I.