2. (16pts) Phosphofructokinase-1 and fructose
bisphosphatase-1 catalyze opposing reactions in a
futile cycle.
A. on the diagram below indicate the positive
and negative allosteric regulators for each
enzyme.
B. Which one is the most important allosteric regulator?
C. Why is it the most important?
D. What is the kinetic evidence to support your model in answer A?
Diagram rate curves (v vs [S]) for both enzymes
indicating the effects of substrates and
allosteric regulators. If the enzyme has two
substrates, draw rate curves for both substrates.
3. (10pts) Explain why ATP has a high negative free energy for group transfer (eg, phosphoryl or adenylyl) to water.
4. (8pts) Phosphoribose isomerase catalyzes interconversion of ribulose-5p and ribose-5P. Draw the mechanism of the reaction showing the transition state intermediate. Indicate the nature and likely amino acid candidates for the catalytic groups in the enzyme.
5. (10pts) Draw the reaction mechanism for aldolase showing the transition state intermediates. Indicate the nature and likely amino acid candidates for the catalytic groups in the enzyme.
6. (10pts) For the enzyme succinyl-CoA synthetase:
A show the steps involved in the conservation of
the free energy of the thioester in the formation
of a phosphoanhydride bond in GTP.
B. Given the standard free energy for hydrolysis
of succinyl-CoA is -40 kJ/mol and the free energy
for hydrolysis of GTP is -32 kJ/mol, what is the
standard free energy change for the reaction
catalyzed by succinyl-CoA synthetase?
7. (6pts) The enzymes isocitrate dehydrogenase, malic enzyme and 6-phosphogluconate dehydrogenase all catalyze an oxidative decarboxylation. Diagram how this works for 6-phosphogluconate dehydrogenase. Show the transition state and the nature of the catalytically important group(s).
8. (8pts) the decarboxylation of
alpha-ketoacids such as pyruvate is a difficult
reaction. Examples are the reactions catalyzed
by pyruvate decarboxylase and the pyruvate
dehydrogenase complex.
Diagram the mechanism for the thiamin
pyrophosphate-dependent decarboxylation of
pyruvate.
9. (8pts) The enzymes enolase and fumarase catalyze the reversible addition of water across a double bond. Diagram the mechanism for this type of reaction.
10. (10pts) Discuss the medical and biochemical consequences to a newborn infant of a genetic defect in the enzyme galactose-1P: UDPGlc uridylyl transferase.
The Rodney Bowling Memorial Possible Bonus page. If you did really, really, poorly on questions 1-10, tell me what you know that I didn't ask.