Abstract:Cytosolic pyruvate kinase (PKc) activity in both mature and young leaves of Passiflora eclulis Smis was inhibited by Zn2+, and the severity of inhibition was dependant upon the concentration of Mg2+ present in the solution . Some differences in the inhibitory kinetics existed between PKc in mature and young leaves. Zn2+ showed anti-competitive inhibition of PKc in both mature and young leaves with respect to PEP and ADP, Ki′ (PEP) were 0. 059 mmol/L and 0. 038 mmol/L, and Ki′ (ADP) were 0. 074 mmol/L and 0.02 mmol/L respectively for PKc in mature and young leaves. Ki (Mg2+) of Zn2+ on PKc in both mature and young leaves were 0. 016 mmol/L and 0. 008 mmol/L respectively. These results further substantiated our previous conclusion that the in regulatory properties of PKc in mature leaves were different from those in young leaves.