Cyclic adenosine 3',5'-monophosphate and luteinizing hormone stimulated protein kinase from bovine corpus luteum: evidence for activation through separate mechanisms.

Protein kinases catalyze the transfer of the terminal phosphate of ATP to a variety of acceptor proteins [ 11. It has been demonstrated that cyclic adenosine 3’, 5’-monophosphate (cyclic AMP) activates protein kinase (holoenzyme, RC) by forming a complex with the regulatory subunit (R) to release the catalytic subunit (C) in the active state [2,3]. In a previous communication from this laboratory the purification and properties of two protein kinases (KI and KII) from bovine corpus luteum has been described [4]. In addition to stimulation by cyclic AMP, KII was also stimulated directly by luteinizing hormone (LH). From these studies it was inferred that LH may have a direct control on the activity of KII and that this effect is independent of cyclic AMP. The present investigation was undertaken to compare the effect of LH with that of cyclic AMP on the stimulation of KII from bovine corpus luteum. Evidence is presented to suggest that cyclic AMP stimulates the activity of KII by binding to the regulatory subunit thereby releasing the activated catalytic subunit whereas LH acts without dissociating the regulatory-catalytic subunit complex.