| Abstract: | Protein kinases (EC 2.7.1.37) were eluted by 0.4 NaCl from chromatin of several mammalian cell typs. The enzymes were partially purified by ion-exchange chromatography, DNA-cellulose columns and sucrose gradient centrifugation. At least five different enzymes could be distinguished by their biochemical properties and their substrate specificities. Three of the enzyme activities tested phosphorylate different sets of histones, while two enzymes phosphorylate acidic nonhistone chromatin proteins or artificial substrates like casein and phosvitin. The two nonhistone protein kinases have slightly different pH and salt optima. They sediment through sucrose gradients with approx. 4 S and approx. 8 S, respectively. These enzymes are further characterized by their different substrate specificity, since they phosphorylate different, though partially overlapping sets of nonhistone chromatin proteins. Enzymes with these properties were deteced in chromatin from mouse ascites cells, bovine lymphocytes, African green monkey kidney cells and a human SV40 transformed cell line. |
