A cyclic AMP-dependent protein kinase from frog bladder epithelial cells

A protein kinase which catalyzes a cyclic AMP-dependent phosphorylation of histone was found in extracts prepared from frog bladder isolated epithelial cells. The enzyme content of these cells is high as compared to the contents reported for several other types of tissue. About 30% of the total activity present in crude extracts is associated with a particulate fraction; 70% is recovered in the cytoplasmic fraction. The characteristics of the cytoplasmic enzyme are very similar to those of protein kinases purified from mammalian tissues. This enzyme's apparent Km for cyclic AMP (10 −8 M) is in the range of the intracellular concentrations measured in the bladder; this suggests that a protein kinase could be involved in the two cyclic AMP-mediated effects of neurohypophysial hormones on this epithelium, namely, increased osmotic water permeability and stimulation of active sodium transport.