[Creatine kinase from muscle cell nuclei].

It has been firstly demonstrated that rat heart and skeletal muscle nuclei contain creatine dinase, one of the most important enzymes of energy metabolism. The nuclei isolated in concentrated sucrose were practically free from cytoplasm and mitochondrial fragments. Electrophoresis in acetyl cellulose revealed that the nuclear extracts from rat heart and skeletal muscles contain only one isoenzyme of creatine kinase similar in mobility to the mitochondrial isoenzyme. The magnitude of Km values for creatine kinase from the nuclei of both tissues was determined. It was shown histochemically that creatine kinase is localized inside the nuclei, predominantly in the sites of chromatin location. A possible role of the enzyme in nuclear metabolism is discussed.