Bacteria such as Escherichia coli use the enzyme glutamine synthetase to produce L-glutamine from glutamate and ammonium ions in the environment. E. coli can also use external L-glutamine as a direct nutrient source. When an external source of L-glutamine is not available, this bacterium synthesizes it using glutamine synthetase.
A scientist investigated the effect of an increase in the concentration of L-glutamine on the activity of glutamine synthetase in this bacterium. He prepared several liquid medium cultures. Each liquid culture had the same volume. He grew each culture in a different concentration of L-glutamine.
In each culture:
Table 1 shows the scientist's results.
| Concentration of L-glutamine / μg cm−3\mu\text{g cm}^{-3}μg cm−3 | Glutamine synthetase activity / arbitrary units | Concentration of L-glutamine remaining in liquid medium / μg cm−3\mu\text{g cm}^{-3}μg cm−3 |
|---|---|---|
| 0 | 80 | 0 |
| 10 | 55 | 0 |
| 20 | 30 | 0 |
| 30 | 10 | 0 |
| 40 | 0 | 8 |
| 50 | 0 | 18 |
| 60 | 0 | 28 |
Apart from temperature and pH, give two variables the scientist would have controlled when preparing the liquid medium cultures.
A student concluded from these results that L-glutamine inhibits glutamine synthetase activity in all bacteria. Use all the information to evaluate the student's conclusion.
Glutamine synthetase catalyses the synthesis of L-glutamine, which requires 1 molecule of ATP for each molecule of glutamine produced. When L-glutamine inhibits glutamine synthetase activity, the bacteria may benefit. Explain how.
