Characterization of the covalent enzyme intermediates formed during pyruvate phosphate dikinase catalysis

The intermediacy of a pyrophosphorylenzyme (E-PP) and phosphorylenzyme (E-P) in the Clostridium symbiosum pyruvate phosphate dikinase catalyzed interconversion of adenosine 5'-triphosphate (ATP), orthophosphate (Pi), and pyruvate with adenosine 5'-monophosphate (AMP), inorganic pyrophosphate (PPi), and phosphoenolpyruvate (PEP) was examined using transient kinetic techniques. Single-turnover experiments with [gamma-32P]ATP or [14C]ATP and PPDK were carried out in the presence and absence of Pi to test for pyrophosphorylenzyme and AMP formation, respectively. Formation of the E-PP.AMP complex was found to be followed by Pi binding and the formation of the E-P.AMP.PPi complex. The level of pyrophosphorylenzyme accumulated during a single turnover was found to be dependent on the divalent metal cofactor used (Mn2+ > Co2+ > Mg2+). Single-turnover experiments with [32P]PEP and PPDK were carried out in the presence and absence of PPi and pyruvate to test for phosphorylenzyme formation in the reverse, ATP-forming direction of the reaction. Phosphorylenzyme formed from the reaction of the E.PEP complex was converted in the presence of AMP and PPi to free enzyme at a rate exceeding the steady-state turnover rate. The reaction sequence for pyruvate phosphate dikinase was determined to be [formula see text] 31P NMR analysis of the phosphorylenzyme in the native (-4.0 ppm) and denatured form (-3.9 ppm) revealed a 3-N-phosphohistidine residue. Complexation of Mg2+ resulted in a 0.3 ppm upfield shift of the phosphorus resonance from native phosphorylenzyme while Mn2+ complexation lead to extensive line broadening, indicative of metal cofactor binding in close vicinity to the phosphoryl group.(ABSTRACT TRUNCATED AT 250 WORDS)