Abstract
Cyclic AMP‐dependent protein kinase and ^3^H‐cAMP‐binding activities were determined in normal Balb 3T3 cells and compared with the same preparations from SV40, chemical, and spontaneous transformants of 3T3 cells. The cytosolic protein kinase activities and protein kinase activity ratios were similar in all cell lines, although when the normal 3T3 cytosol was prepared by homogenization it contained less ^3^H‐cAMP binding activity than the transformed 3T3 cytosols. The Triton X‐100 treated particulate fractions from the normal and transformed 3T3 cells contained similar protein kinase and binding activities.
The isozymic profile of cAMP‐dependent protein kinases was examined by DEAE‐chromatography. The 3T3 cells contained only type II isozyme in either cytosolic or membrane fractions. All transformants of the 3T3 cells contained both type I and type II isozymes. Other cell cultures, including chicken embryo fibroblasts, rat kidney cells, and human or calf endothelial cells contained type I and type II isozymes.
Binding of the photoaffinity analogue of cAMP, 8‐N~3~ cAMP, to the regulatory subunits of protein kinases in sonicates obtained from Balb 3T3 and SV 3T3 cells followed by separation on SDS polyacrylamide electrophoresis showed that the amount of R~II~ subunit was approximately equal in the two cell lines. R~I~ in Balb 3T3 cells was detectable but in a much lower quantity than in SV 3T3 cells.
The cyclic AMP dependent‐protein kinases from Balb 3T3 cells appear to be different from SV 3T3 cells by three criteria: ^3^H‐cAMP binding in homogenates, DEAE chromatographic separation of isozymes, and 8‐N~3~ cAMP binding.