Carb metabolism in Thermoproteus: Insights from GAPDH

CHEM3600 Introductory Biochemistry

Task

Carbohydrate metabolism in the thermophilic organism Thermoproteus tenax is different than that of mammals. For example, the PFK-1 catalyzed reaction is reversible. Also, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is regulated. The reaction catalyzed by GAPDH is:

glyceraldehyde-3-phosphate + 2NAD+ + 2Pi ? 1,3-bisphosphoglycerate + NADH

The data given in the graph show GAPDH activity measured in the presence of a constant amount of GAP and Pi and increasing amounts of NAD+. The solid, unlabeled curve is the enzyme in the absence of any regulators. The dotted lines represent enzyme activity in the presence of allosteric regulators glucose-1-phosphate (G1P), AMP, and NADP+.

a. In living T. tenax, GAPDH does not show any activity in the presence of 1,3-bisphosphoglycerate. Based on this observation, what can you say about ΔG’ for this reaction? Briefly explain. (7 pts)

b. Based on the data shown above, are G1P, AMP, and NADP+ activators or inhibitors of GAPDH? How do you know? (3 pts)

c. Draw a curve on the graph depicting the predicted effect of ATP on GAPDH activity. Label all axes correctly and include a curve for GAPDH with no ATP added. Briefly explain. (4 pts)

d. Would you expect fructose-2,6-bisphosphate to be an important regulator of T. tenax glycolysis? Explain briefly. (6 pts)

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