Crystallization and preliminary X-ray diffraction studies of C₄-form phosphoenolpyruvate carboxylase from maize

Phosphoenolpyruvate carboxylase is a key enzyme in the fixation of atmospheric CO₂ in C₄ and crassulacean acid metabolism (CAM) plants. The enzyme catalyzes the irreversible carboxylation of phosphoenolpyruvate to form oxaloacetate and inorganic phosphate, the first committed step in the fixation of external CO₂ in these plants. The enzyme has been isolated from maize leaves and crystallized using the hanging-drop vapour-diffusion method with PEG 8000 as a precipitant at pH 7.5. The crystals belong to space group C222₁, with unit-cell dimensions a = 160.2, b = 175.6, c = 255.5 Å, and diffract to 3.2 Å resolution.