NAD+ -dependent Glyceraldehyde-3-phosphate + Dehydrogenase from Thermoproteus tenax. 1. Name the three enzymes that catalyze irreversible,...

NAD+ -dependent Glyceraldehyde-3-phosphate + Dehydrogenase from Thermoproteus tenax.

1. Name the three enzymes that catalyze irreversible, regulated reactions in glycolysis as studied in class.

2. What is the significance of the GAPDH reaction in E. coli to glycolysis?

3. How does the reaction catalyzed by GAPDH from T. tenax presented here differ from the reaction carried out in E. coli?

4. The activity of the GAPDH enzyme was assayed in the presence of a constant amount of glyceraldehyde-3-phosphate and an increasing amount of NAD . The activity of the control was + compared to the activity in the presence of various metabolites. The results are shown in Figure 20.2. Additional data are given in Table 20.2.

a. Use the data in Figure 20.2 to estimate a KM value for the enzyme in the presence of these metabolites. Classify the metabolites listed in Table 20.2 as inhibitors or activators. Fill in your answers in the table provided. Explain how you decided whether these metabolites are inhibitors or activators, based on the graph.

b. How would you classify NADH, ADP and ATP? (These data are not presented in the graph). Are they inhibitors or activators? Add this information to Table 20.2.

c. Explain the physiological significance of your answers to questions 4a and 4b. NAD+ -dependent Glyceraldehyde-3-phosphate + Dehyd

5. In the absence of NADP+, the binding of NAD+ to the T. tenax GAPDH showed no cooperative binding (closed circles, Figure 2 above). In the presence of NADP however, the binding of NAD+ to the T. tenax GAPDH was found to have a Hill coefficient of 2 (open circles, Figure 2 above).

a) What is the significance of the change in the value of the Hill coefficient?

b) Is this consistent with the shape of the curve and the information given in the background concerning the enzyme's quaternary structure?

6. What is the ATP yield for one mole of glucose oxidized by the pathway that uses the non-phosphorylating GAPDH enzyme?

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gladiator answered 11 months ago

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