REACTION-MECHANISM OF PYROPHOSPHATE-DEPENDENT PHOSPHOFRUCTOKINASE FROM PINEAPPLE LEAVES

Data obtained from initial velocity, product inhibition and dead-end inhibition patterns indicate that the pyrophosphate-dependent phosphofructokinase from pineapple leaves has a rapid equilibrium random mechanism with E:F6P:MgPP(i) and E:MgPP(i):FBP dead-end complexes. The pH dependence of enzyme-reactant dissociation constants suggests that phosphates of F6P (fructose 6-phosphate), FBP (fructose 1, 6-bisphosphate), P(i) and PP(i) must be completely ionized and the lysine is present in the vicinity of the 1- and 6-phosphates of the sugar phosphate and bisphosphate. The pH dependence of kinetic parameters suggests that the enzyme catalyzes the reaction via general acid-base catalysis with the use of a proton shuttle. The base is required to be unprotonated in both reaction directions.