Cyclic 3',5'-AMP-Dependent Protein Kinase Activity in Toad Bladder Epithelium 1

Summary

A cyclic AMP-dependent protein kinase was partially purified from toad urinary bladder epithelium. Cyclic AMP-stimulated protein kinase activity as well as the unstimulated (control) activity of the enzyme was maximal at pH 6.5 using Tris-maleate, sodium cacodylate or sodium acetate buffers. The apparent K_m value of cyclic AMP for the stimulation of the enzyme (in sodium acetate buffer and in the presence of 10 mM Mg²⁺) was 1.5 × 10^-9 M. The acyclic nucleotide 5'-AMP (in the concentration range 5 × 10^-10 to 5 × 10^-5 M) failed to activate bladder protein kinase. Ca²⁺ was found to be inhibitory at concentrations higher than 5 × 10^-4 M. A role for cyclic AMP-dependent protein kinase in neurohypophyseal hormone-induced permeability changes is discussed.