HYSTERETIC BEHAVIOR OF PHOSPHOENOLPYRUVATE CARBOXYLASE FROM PANICUM-MAXIMUM

Phosphoenolpyruvate carboxylase isolated from Panicum maximum Jacq. le af presented a hysteretic behaviour that resulted in a kinetical lag i n the reaction progress curve. This lag depended on the concentration of enzyme, total phosphoenolpyruvate (PEP) and total Mg2+. Through an analysis of these dependences it is suggested that the hysteresis is d ue to an association-dissociation process influenced by union, to one form of the enzyme, of more than one of the three possible ligands: fr ee Mg2+, free PEP or PEP-Mg2+ complex. The partially purified enzyme s howed, during steady state, a Michaelis-Menten kinetics for PEP and Mg 2+ (total concentrations) and pH optima between 7.8 and 8.2.