Explain5 marksStandard
A student investigates the effect of two different inhibitors, X and Y, on the activity of the enzyme lactase. They measure the initial rate of reaction (in arbitrary units) at various substrate concentrations. The results are shown in the table below.
| Substrate concentration (mM) | Initial rate – no inhibitor | Initial rate – with inhibitor X | Initial rate – with inhibitor Y |
|---|---|---|---|
| 0.5 | 10 | 6 | 8 |
| 1.0 | 18 | 10 | 14 |
| 2.0 | 30 | 18 | 20 |
| 5.0 | 45 | 32 | 25 |
| 10.0 | 50 | 45 | 26 |
| 20.0 | 52 | 52 | 26 |
The student notes that at high substrate concentrations, the rate with inhibitor X approaches the same maximum rate as without inhibitor, whereas the rate with inhibitor Y reaches a lower maximum rate.
Explain which inhibitor is competitive and which is non-competitive. Use the data to justify your answer.