| Abstract: | A new species of protein kinase has been identified in cytosol preparations from bovine corpora lutea. Enzyme activity required the simultaneous presence of Ca2+ and phospholipid, and was also enhanced by glyceryl dioleate. Phosphatidylserine was the most effective phospholipid for stimulating histone phosphorylation. Other phospholipids capable of supporting enzymic activity were, in order of decreasing activity, phosphatidylinositol, phosphatidic acid, cardiolipin and phosphatidylglycerol. Several other phospholipids tested were ineffective. A cyclic AMP-dependent protein kinase was also present in the luteal cytosol. This enzyme activity was eliminated by protein kinase inhibitor without affecting the Ca2+- and phospholipid-stimulated activity. Lysine-rich histone (IIIS) was a much better substrate than type-IIA histone for Ca2+- and phospholipid-dependent phosphorylation. Ca2+ and phospholipid also enhanced phosphorylation of endogenous luteal cytosol protein. Calmodulin, alone or in the presence of Ca2+, was unable to increase phosphorylation. Trifluoperazine inhibited protein kinase activity stimulated by Ca2+ and phospholipid. These data suggest that a phospholipid-sensitive, Ca2+-dependent protein kinase may provide an important link between hormonally-induced changes in phospholipid metabolism and corpus-luteum function. |
