The acidic peptide-specific type II protein kinases from the nucleus and the cytosol of porcine liver are distinct

Abstract

The second messenger-independent acidic peptide-specific protein kinase II (casein kinase II) from the cytosol of porcine liver has been purified to apparent homogeneity by using DEAE-cellulose, hydroxyl apatite, and phosphocellulose chromatography. The native enzyme has an apparent M r of 150,000. After sodium dodecyl sulfate-gel electrophoresis a band of M r = 39,000 and a slightly diffuse band of M r = 27,000 were found indicating an α 2 β 2 structure of this protein kinase. A thorough comparison with the corresponding enzyme from the nucleus was performed. The two enzymes differ in the subunit composition, as the nuclear enzyme is composed of subunits with a M r of 95,000; they further differ in the heparin sensitivity and binding to blue dextran-Sepharose. Distinct differences in their nucleotide binding sites were found upon mapping with ATP analogs, although both enzymes utilize ATP as well as GTP. On the other hand, both enzymes phosphorylate identical sites in the casein variants βA2 and αS1B at comparable rates. These results demonstrate for the first time the existence of distinct nucleus and cytoplasm specific type II “casein kinases.”