PKA from Saccharomyces cerevisiae can be activated by cyclic AMP and cyclic GMP

Analysis of Saccharomyces cerevisiae genome revealed no sequence homologous to cyclic GMP (cGMP) dependent protein kinase from other organisms. Here w e demonstrate that cyclic AMP (cAMP) dependent protein kinase purified from S. cerevisiae was almost equally activated by cAMP and cGMP at 3 x 10(-6) M concentrations of either nucleotide in the presence of Mg2+ ions. Interes tingly, if Mn2+ ions were used instead of Mg2+, cGMP was only 30% as effect ive as cAMP in the activation of cAMP-dependent protein kinase. Analogs of cAMP such as 8-chloro-cAMP and 3':5'-cyclic monophosphate of ribofuranosylb enzimidazole were as potent as cAMP in the enzyme activation, while N-6,2'- O-dibutyryl-cAMP activated the enzyme to a lower extent. It was also found that yeast cAMP-dependent protein kinase can be activated by limited proteo lytic digestion. The results presented were obtained with protamine and rib osomal protein S10 used as phosphorylation substrates.