Heterogeneity of protein kinase NII. Multiple subunit-polypeptides

Protein kinase NII has a alpha alpha' beta 2 subunit structure, and consists of a chromatographically heterogeneous population. By two-dimensional polyacrylamide gel electrophoresis, each subunit was resolved into multiple polypeptides with various pI values: alpha subunit, 4 spots; alpha' subunit, 10 spots; and beta subunit, 4 spots. NII underwent autophosphorylation on beta subunits. Fractions of alpha and alpha' polypeptides also occurred as phosphoforms as shown by alkaline phosphatase treatment. In addition, alpha' subunit had another motif for heterogeneity, which separated alpha' polypeptides into two groups, and was exemplified by NIIa and NIIb that showed different enzyme kinetics and the nuclear localization. We interpret these to account for the basis of the functional as well as molecular heterogeneities of protein kinase NII.