Heterogeneity of protein kinase NII from rat liver nuclei

Protein kinase NII from rat liver nuclei was resolved into two fractions, NIIa and NIIb, by DEAE-Sephadex column chromatography. NIIa was eluted at 151 mM (NH4)2SO4 and NIIb at 175 mM. They had an identical molecular size (125,000 daltons, 7.0S) and subunit composition (alpha alpha' beta 2). However, they showed significantly different Km values and turnover numbers for casein substrate. Furthermore, NIIa was found predominantly as a form bound to the chromatin, while NIIb was in the nucleoplasmic-soluble fraction in addition to the chromatin-bound fraction. These observations suggest that NII consists of a heterogeneous population of at least two molecular species, differing in the activity and functional states in the cell nucleus.