1. (4 pts) The sweet taste of freshly picked corn is due to the high level of sucrose in the kernels. Store bought corn is not as sweet because about 50% of the sucrose is converted into starch within 1 day of picking. To preserve sweetness freshly picked corn can be immersed in boiling water for a few minutes and then plunged into cold water. Corn processed this way and stored in a freezer preserves its garden fresh sweetness. What is the biochemical basis for this procedure?
2. (4 pts) The following data were obtained for an intestinal dipeptidase that hydrolyzes the dipeptide glycyl-glycine to two glycines.
A: plot v versus [S] and estimate Vmax and Km.
B: plot 1/v versus 1/[S] and calculate Vmax and Km.
| [S] (mM) | v (µmoles/min) |
|---|---|
| 1.5 | 0.21 |
| 2.0 | 0.24 |
| 3.0 | 0.28 |
| 4.0 | 0.33 |
| 8.0 | 0.40 |
| 16.0 | 0.45 |
3. (7 pts) Prostaglandins are a class of eicosanoids that are responsible for producing fever and inflammation and its associated pain. They are produced from the polyunsaturated fatty acid arachidonate by the enzyme prostaglandin endoperoxide synthase, a cyclooxygenase. Ibuprofen is an inhibitor of this enzyme. By inhibiting prostaglandin production it reduces inflammation and pain.
The kinetic data given below are for the prostaglandin endoperoxide synthase in the presence of arachidonate, its substrate, and in the presence and absence of the inhibitor ibuprofen (v-con is the rate for arachidonate alone and v-ibu is the rate in the presence of ibuprofen).
Calculate Vmax and Km in the presence and absence of ibuprofen. What type of inhibitor is ibuprofen?
| [S] (mM) | v-con (mmoles/min) | v-ibu (mmoles/min) |
|---|---|---|
| 0.5 | 23.5 | 16.67 |
| 1.0 | 32.2 | 25.25 |
| 1.5 | 36.9 | 30.49 |
| 2.5 | 41.8 | 37.04 |
| 3.5 | 44.0 | 38.91 |