Partial purification and kinetic characterization of transaldolase from Dictyostelium discoideum

Transaldolase was purified 42-fold from Dictyostelium discoideum and the resulting preparation exhibited stoichiometry. Kinetic analyses consisted of initial velocity and product inhibition studies in both the forward and the reverse directions. The enzyme exhibited ping-pong kinetics with sedoheptulose 7-phosphate adding first and erythrose 4-phosphate releasing first. The K m values for sedoheptulose 7-phosphate, glyceraldehyde 3-phosphate, erythrose 4-phosphate, and fructose 6-phosphate were 0.46, 0.072, 0.10, and 1.6 m M, respectively. The K i values for sedoheptulose 7-phosphate and erythrose 4-phosphate were 3.6 and 0.062 m M, respectively. Inorganic phosphate inhibited enzymatic activity and showed mixed-type inhibition when fructose 6-phosphate was varied. A K i value of 35.2 m M was determined for inorganic phosphate.