Purification and characterization of the catalytic subunit of cAMP dependent protein kinase from Drosophila melanogaster

Polyethylenimine selectivity precipitates a large fraction of the proteins present in a crude Drosophila embryonic extract. While the free catalytic subunit of the cAMP dependent protein kinase is quantitatively retained in the soluble fraction after polyethylenimine precipitation, the rest of the abundant and highly active protein kinases present in the embryo are quantitatively precipitated. The catalytic subunit of the cAMP dependent protein kinase was purified until apparent homogeneity from the soluble protein fraction after polyethylenimine precipitation. The pH optimum of the purified enzyme is 6.3. While magnesium is the preferred divalent cation for all the cAMP dependent protein kinases described previously, the Drosophila enzyme is three times more active if manganese is present as divalent cation compared with magnesium. The enzyme is tost active between 50–100 mM monovalent ion concentration. Heparin can selectively modulate the phosphorylation of different substrate proteins.