Purification and subunit composition of guanosine 3':5'-monophosphate-dependent protein kinase from bovine lung

The guanosine 3':5'-monophosphate-dependent protein kinase from bovine lung was purified to apparent homogeneity by affinity chromography using 8-2-aminoethylthio-cGMP coupled to Sepharose 4B. The kinase activity was purified approximately 6000-fold with an overall recovery of approximately 20%. The product isolated by affinity chromatography contained both cGMP-binding and cGMP-dependent histone kinase activity, indicating that the enzyme was not dissociated into regulatory and catalytic components by the immobilized cGMP derivative. The enzyme had a molecular weight of approximately 165,000 and a sedimentation coefficient of 7.8 S. The purified kinase displayed several characteristics similar to that of the partially purified enzyme including specificity for cGMP and stimulation by high concentrations of magnesium. On sodium dodecyl sulfate gels, only one major polypeptide chain was present having a molecular weight of approximately 81,000. This subunit bound 1 mol of cGMP and exhibited cGMP-dependent protein kinase activity. It is proposed that the native enzyme consists of two identical subunits (Mr=81,000), each of which binds cGMP and catalyzes protein phosphorylation.