Purification and Properties of a Protein Kinase from Bovine Corpus Luteum That Is Stimulated by Cyclic Adenosine 3′,5′-Monophosphate and Luteinizing Hormone

A protein kinase has been purified from the bovine corpus luteum by acid precipitation, ammonium sulfate fractionation and chromatography on DEAE-cellulose and hydroxylapatite columns. The enzyme has a molecular weight of approximately 159,000. DEAE-cellulose chromatography resolved the protein kinase activity into two peaks, designated as KI and KII. Both peaks possessed adenosine 3',5'-monophosphate (cyclic AMP)-binding activities and both kinase activities were stimulated in vitro by cyclic AMP. The extent of stimulation of KII by cyclic AMP was greater than that of KI. (Km for cyclic AMP, 2.0 x 10-8 m.) KII was further purified by chromatography on hydroxylapatite. In addition to stimulation by cyclic AMP, the enzyme recovered from hydroxylapatite was also stimulated by luteinizing hormone (LH) in vitro. The response to LH was concentration dependent and specific. Other pituitary hormones were ineffective. The effects of LH and cyclic AMP were not additive and the binding of cyclic [3H]AMP to the hydroxylapatite-treated enzyme was not inhibited by the presence of LH. It is concluded that LH may have a direct control on the activity of protein kinase in the corpus luteum that is independent of cyclic AMP.