Figure 4.

Loss of response to neutral amino acids of the ZmPEPC-C₄ S100K mutant. A and B, saturation by Gly in the absence (A) or presence of 20 mm l-malate (B) of the WT and S100K mutant enzymes. C and D, saturation by l-Ala and l-Ser, respectively, of the WT and S100K mutant enzymes. Initial velocity data are depicted as black circles (WT) or red circles (S100K mutant). Activity assays were carried out at pH 7.4 and 30 °C, 3 mm total PEP, 0.4 mm free Mg²⁺, and 0.1 mm bicarbonate; 20 mm l-malate was included in the assay medium where indicated. The results are mean values from two independent experiments. The points in the figures are the experimentally determined values, whereas the curves are calculated from fits of these data to Equation 1 given under “Experimental procedures.” Error bars represent S.E.; prot., protein.