Explain5 marksChallenge
An enzyme (X) from yeast catalyses the conversion of substrate Y into product Z. The initial rate of reaction was measured at various substrate concentrations, both in the absence of any inhibitor and in the presence of a fixed concentration of an unknown reversible inhibitor (I). The results are shown in the table below.
| Substrate concentration (mM) | Rate without inhibitor (arbitrary units) | Rate with inhibitor (arbitrary units) |
|---|---|---|
| 0.5 | 20 | 8 |
| 1.0 | 33 | 14 |
| 2.0 | 50 | 25 |
| 5.0 | 67 | 40 |
| 10.0 | 77 | 53 |
| 20.0 | 83 | 62 |
| 50.0 | 86 | 71 |
| 100.0 | 87 | 75 |
From the data, the maximum rate (Vmax) for the uninhibited reaction is estimated to be 90 arbitrary units, and that for the reaction with inhibitor is also 90 arbitrary units. The Michaelis-Menten constant (Km) for the uninhibited reaction is approximately 2.0 mM, whereas for the reaction with inhibitor it is approximately 5.0 mM.
Explain whether the inhibitor I is a competitive or non-competitive inhibitor.