Cyclic AMP-dependent protein kinases and cAMP-binding proteins in human mammary tumor MCF-7 cells

Two isoenzymes of cAMP-dependent protein kinases were found in MCF-7 cytosol. The regulatory (cAMP-binding) subunit of protein kinase I (predominant form) has an apparent molecular weight (MW) of 49,000 and the two forms of regulatory subunits of protein kinase II have MWs of 52,000 and 54,000. Substantial amounts of the 49,000 protein cochromatographed on DEAE cellulose with protein kinase II. The quantities of protein kinase holoenzyme activity are strongly influenced by extraction procedures: the use of EDTA and of the protease inhibitor benzamidine can lead to extensive dissociation. On the other hand, high yields of cAMP-dependent protein kinase holoenzyme activity were consistently obtained with 150 mM KCl.