Figure 4.

Dependence of the ATPase activity of various MetNI constructs on the concentration of methionine analogues. The ATPase activity was measured from the rate of phosphate production as assayed by the method of Webb (41), and converted to moles phosphate/minute/mole transporter. An initial ATP concentration of 1 mM was used, which is ∼3 times the apparent K_m (Figure S3). The blue diamonds, black squares and green triangles correspond to L-methionine, D-methionine and L-selenomethionine, while the open blue and red circles represent the effect of L-methionine on the E166Q (ATPase-inactive mutant) and the ΔC2-MetNI truncation mutant, respectively. The error bars represent the standard deviations calculated from 8 measurements.