Competitive Inhibition

Practice: Which of the following would be altered on a Lineweaver-Burk plot in the presence of a competitive inhibitor?

Practice: N-hydroxy-L-arginine (an intermediate in nitric oxide biosynthesis) can bind to the active site of arginase making its manganese reactive metal center unavailable for catalysis. How would an increased concentration of this intermediate be expected to affect the kinetic parameters of this enzyme?

Practice: An enzyme has a K_m of 8 μM in the absence of a competitive inhibitor and a K _𝐦^𝐚𝐩𝐩 of 12 μM in the presence of 3 μM of the inhibitor. Calculate the K_I.

Practice: Use the Lineweaver-Burk plot below to answer the following questions. Units of [S] are in nM.

A) Estimate the values of K_m & V_max as well as the K_𝐦^𝐚𝐩𝐩 & V_𝐦𝐚𝐱^𝐚𝐩𝐩 for the reactions in the absence and presence of the competitive inhibitor.

B) Would you expect the competitive inhibitor to be more effective under conditions of high or low [S]? Why?

C) If [I] = 10 nM, calculate the inhibition constant (K _I).