Two inhibitors of the same enzyme, inhibitor A and inhibitor B, were investigated to discover if they were competitive or non-competitive. In order to do this, the rate of reaction of the enzyme was measured at different concentrations of substrate without inhibitor, with inhibitor A and with inhibitor B. Graphs of the data were plotted as shown on the next page. The graphs showed that one inhibitor was competitive and the other non competitive.

Copy the graphs.

a. Label the graph for ‘no inhibitor’ to show the position of Vmax, ½Vmax and Km.

b. State the effect that inhibitor A had on Vmax and Km of the enzyme.

c. State the effect that inhibitor B had on Vmax and Km of the enzyme.

d. Which inhibitor is competitive and which is non-competitive? Explain your answer.

Double-reciprocal plots of the data obtained produced the following graphs.

e. Identify which line, X, Y or Z, corresponds to each of the following experiments:

i. Inhibitor absent

ii. Competitive inhibitor present

iii. Non-competitive inhibitor present

Briefly explain your answers to ii and iii.

Transcribed Image Text:

no inhibitor inhibitor A inhibitor B V v= velocity (rate) [S] = substrate concentration [S]