FIGURE 4.

Inhibition of isoleucine activation by mupirocin in the reactions by SgIleRS or ScIleRS. A, activation by SgIleRS using 3.9, 7.8, 15.6, 39, and 78 μm isoleucine and 0 (●), 5 (■), 10 (▴), 20 (▾), and 30 mm (♦) mupirocin. B, activation by ScIleRS using 2 (●), 5 (■), 10 (▴), 20 (▾), and 50 μm (♦) isoleucine and 0, 20, 50, 100, and 200 μm mupirocin. The inhibition constants were determined by fitting the data to competitive inhibition model using GraphPad Prism. The values represent the best fit value ± S.E. of two independent experiments. C, Lineweaver-Burk plots depict a competitive inhibition pattern for both enzymes.