title: Phosphorylation and inactivation of yeast fructose-1,6-bisphosphatase by cyclic AMP-dependent protein kinase from yeast.
abstract: Purified fructose-1,6-bisphosphatase from Saccharomyces cerevisiae was phosphorylated in vitro by purified yeast cAMP-dependent protein kinase. Maximal phosphorylation was accompanied by an inactivation of the enzyme by about 60%. In vitro phosphorylation caused changes in the kinetic properties of fructose-1,6-bisphosphatase: 1) the ratio R(Mg2+/Mn2+) of the enzyme activities measured at 10 mM Mg2+ and 2 mM Mn2+, respectively, decreased from 2.6 to 1.2; 2) the ratio R(pH 7/9) of the activities measured at pH 7.0 and pH 9.0, respectively, decreased from 0.62 to 0.38, indicating a shift of the pH optimum to the alkaline range. However, the affinity of the enzyme for its inhibitors fructose-2,6-bisphosphate (Fru-2,6-P2) and AMP, expressed as the concentration required for 50% inhibition, was not changed. The maximum amount of phosphate incorporated into fructose-1,6-bisphosphatase was 0.6-0.75 mol/mol of the 40-kDa subunit. Serine was identified as the phosphate-labeled amino acid. The initial rate of in vitro phosphorylation of fructose-1,6-bisphosphatase, obtained with a maximally cAMP-activated protein kinase, increased when Fru-2,6-P2 and AMP, both potent inhibitors of the enzyme, were added. As Fru-2,6-P2 and AMP did not affect the phosphorylation of histone by cAMP-dependent protein kinase, the inhibitors must bind to fructose-1,6-bisphosphatase in such a way that the enzyme becomes a better substrate for phosphorylation. Nevertheless, Fru-2,6-P2 and AMP did not increase the maximum amount of phosphate incorporated into fructose-1,6-bisphosphatase beyond that observed in the presence of cAMP alone.
mesh_terms: D000249:Adenosine Monophosphate / Q000494:pharmacology; D006597:Fructose-Bisphosphatase / Q000378:metabolism*; D005635:Fructosediphosphates / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D010766:Phosphorylation; D011494:Protein Kinases / Q000494:pharmacology*; D015003:Yeasts / Q000201:enzymology*
chemical_list: D005635:Fructosediphosphates; D000249:Adenosine Monophosphate; D008345:Manganese; C027652:fructose 2,6-diphosphate; D011494:Protein Kinases; D006597:Fructose-Bisphosphatase; D008274:Magnesium