A student investigated the effect of pH on the digestion of protein by the stomach enzyme pepsin. The student mixed a cloudy egg-white (protein) suspension with pepsin inside test tubes containing buffer solutions at various pH levels, and recorded the time taken for the suspension to turn completely clear.
| pH of buffer solution | Time taken for protein suspension to clear (minutes) |
|---|---|
| 1.5 | 3 |
| 3.0 | 7 |
| 5.0 | 14 |
| 8.5 | Suspension remained cloudy after 30 minutes |
Explain why the protein was not digested in the tube at pH 8.5.