3.9 Inhibitor kinetics A pesticide inhibits the activity of a particular enzyme A, which can therefore be used to assay for the presence of the pesticide in an unknown sample. (a) In the laboratory, the initial rate data shown in Table 3P9.1 were obtained. Is the pesticide a competitive or noncompetitive inhibitor? Evaluate K,.vma, and K.. (b) After 50 ml of the same enzyme solution in part (a) is mixed with 50 ml of 8 x 10- M substrate and 25 mL of sample, the initial rate observed is 18 umol/min. What is the pesticide concen- tration in the unknown assuming no other inhibitors or substrates are present in the sample? THE KINETICS OF ENZYME-CATALYZED REACTIONS 155 Table 3P9.1 v, mol/(L-min) x 10 s, mol/L No inhibitor 10-3 M inhibitor 3.3 x 10* 5.0 x 10 6.7 x 10 1.65 x 10-3 2.21 x 10-3 56 37 71 47 88 61 129 103 149 125