Corn leaf phosphoenolpyruvate carboxylases: Purification and properties of two isoenzymes

Two phosphoenolpyruvate carboxylase proteins (PC-I and PC-II) were extracted and purified close to homogeneity from corn leaves. PC-I contained about 85% and PC-II about 15% of the total phosphoenolpyruvate carboxylase activity. PC-I eluted from a DEAE-cellulose column with a buffer having lower ionic strength, had higher K_m and V values with respect to phosphoenolpyruvate, Mg²⁺, and Mn²⁺, was more thermolabile and moved more slowly toward the anode during disc gel electrophoresis as compared to PC-II. The enzymes had sedimentation coefficient values (s_20,W) of 9.7 and 11.6S and molecular weights, determined by equilibrium centrifugation on sucrose density gradients, of 225,650 and 270,800, respectively. The enzymes used HCO₃^? as the active “CO₂” substrate, and the major protein (PC-I) had a temperature optimum for activity of 40 °C.