Abstract
Protein kinases were separated from rat kidney nuclear extract by hydroxylapatite column chromatography. Five (I-V) different protein kinases were isolated when histone was used as a substrate. Two (I and III) of them stimulated phosphorylation of c-erb A-β protein (50 kDa) expressed in Escherichza coli. The c-erb A product has an activity of high affinity T3 binding. One (I) of the kinases was dependent on cyclic adenosine 3', 5'-monophosphate (cyclic AMP). The other kinase (III) was not dependent on cyclic nucleotides. The latter kinase was eluted from hydroxylapatite column with 0.05 M PO4 at pH 7.4. The sedimentation coefficient (s) estimated by continuous sucrose density gradient centrifugation was approximately 6.0.Km values for ATP were estimated by double reciprocal analyses, which gave 110.0μM in the protein kinase I (in the presence of 10-6M cyclic AMP) and 25μM in the protein kinase III, respectively. The data showed that 1.0 mol phosphate was incorporated into 80 mol of c-erb A protein (50kDa) either in the presence of protein kinase I (with 10-6M cyclic AMP) or in the presence of protein kinase III. These results suggested that there are protein kinases for c-erb A protein, whose functional properties are similar to those of nuclear T3receptor, in rat kidney nuclei.
